diff --git a/src/PhpSpreadsheet/Calculation/DateTime.php b/src/PhpSpreadsheet/Calculation/DateTime.php
index 4c2b108ad9..64d72c2b58 100644
--- a/src/PhpSpreadsheet/Calculation/DateTime.php
+++ b/src/PhpSpreadsheet/Calculation/DateTime.php
@@ -144,26 +144,10 @@ private static function adjustDateByMonths($dateValue = 0, $adjustmentMonths = 0
      */
     public static function DATETIMENOW()
     {
-        $saveTimeZone = date_default_timezone_get();
-        date_default_timezone_set('UTC');
-        $retValue = false;
-        switch (Functions::getReturnDateType()) {
-            case Functions::RETURNDATE_EXCEL:
-                $retValue = (float) Date::PHPToExcel(time());
+        $dti = new DateTimeImmutable();
+        $dateArray = date_parse($dti->format('c'));
 
-                break;
-            case Functions::RETURNDATE_UNIX_TIMESTAMP:
-                $retValue = (int) time();
-
-                break;
-            case Functions::RETURNDATE_PHP_DATETIME_OBJECT:
-                $retValue = new \DateTime();
-
-                break;
-        }
-        date_default_timezone_set($saveTimeZone);
-
-        return $retValue;
+        return is_array($dateArray) ? self::returnIn3FormatsArray($dateArray) : Functions::VALUE();
     }
 
     /**
@@ -185,27 +169,10 @@ public static function DATETIMENOW()
      */
     public static function DATENOW()
     {
-        $saveTimeZone = date_default_timezone_get();
-        date_default_timezone_set('UTC');
-        $retValue = false;
-        $excelDateTime = floor(Date::PHPToExcel(time()));
-        switch (Functions::getReturnDateType()) {
-            case Functions::RETURNDATE_EXCEL:
-                $retValue = (float) $excelDateTime;
-
-                break;
-            case Functions::RETURNDATE_UNIX_TIMESTAMP:
-                $retValue = (int) Date::excelToTimestamp($excelDateTime);
+        $dti = new DateTimeImmutable();
+        $dateArray = date_parse($dti->format('c'));
 
-                break;
-            case Functions::RETURNDATE_PHP_DATETIME_OBJECT:
-                $retValue = Date::excelToDateTimeObject($excelDateTime);
-
-                break;
-        }
-        date_default_timezone_set($saveTimeZone);
-
-        return $retValue;
+        return is_array($dateArray) ? self::returnIn3FormatsArray($dateArray, true) : Functions::VALUE();
     }
 
     /**
@@ -316,14 +283,8 @@ public static function DATE($year = 0, $month = 1, $day = 1)
 
         // Execute function
         $excelDateValue = Date::formattedPHPToExcel($year, $month, $day);
-        switch (Functions::getReturnDateType()) {
-            case Functions::RETURNDATE_EXCEL:
-                return (float) $excelDateValue;
-            case Functions::RETURNDATE_UNIX_TIMESTAMP:
-                return (int) Date::excelToTimestamp($excelDateValue);
-            case Functions::RETURNDATE_PHP_DATETIME_OBJECT:
-                return Date::excelToDateTimeObject($excelDateValue);
-        }
+
+        return self::returnIn3FormatsFloat($excelDateValue);
     }
 
     /**
@@ -403,36 +364,24 @@ public static function TIME($hour = 0, $minute = 0, $second = 0)
         }
 
         // Execute function
-        switch (Functions::getReturnDateType()) {
-            case Functions::RETURNDATE_EXCEL:
-                $date = 0;
-                $calendar = Date::getExcelCalendar();
-                if ($calendar != Date::CALENDAR_WINDOWS_1900) {
-                    $date = 1;
-                }
-
-                return (float) Date::formattedPHPToExcel($calendar, 1, $date, $hour, $minute, $second);
-            case Functions::RETURNDATE_UNIX_TIMESTAMP:
-                return (int) Date::excelToTimestamp(Date::formattedPHPToExcel(1970, 1, 1, $hour, $minute, $second)); // -2147468400; //    -2147472000 + 3600
-            case Functions::RETURNDATE_PHP_DATETIME_OBJECT:
-                $dayAdjust = 0;
-                if ($hour < 0) {
-                    $dayAdjust = floor($hour / 24);
-                    $hour = 24 - abs($hour % 24);
-                    if ($hour == 24) {
-                        $hour = 0;
-                    }
-                } elseif ($hour >= 24) {
-                    $dayAdjust = floor($hour / 24);
-                    $hour = $hour % 24;
-                }
-                $phpDateObject = new \DateTime('1900-01-01 ' . $hour . ':' . $minute . ':' . $second);
-                if ($dayAdjust != 0) {
-                    $phpDateObject->modify($dayAdjust . ' days');
-                }
+        $retType = Functions::getReturnDateType();
+        if ($retType === Functions::RETURNDATE_EXCEL) {
+            $date = 0;
+            $calendar = Date::getExcelCalendar();
+            if ($calendar != Date::CALENDAR_WINDOWS_1900) {
+                $date = 1;
+            }
 
-                return $phpDateObject;
+            return (float) Date::formattedPHPToExcel($calendar, 1, $date, $hour, $minute, $second);
         }
+        if ($retType === Functions::RETURNDATE_UNIX_TIMESTAMP) {
+            return (int) Date::excelToTimestamp(Date::formattedPHPToExcel(1970, 1, 1, $hour, $minute, $second)); // -2147468400; //    -2147472000 + 3600
+        }
+        // RETURNDATE_PHP_DATETIME_OBJECT
+        // Hour has already been normalized (0-23) above
+        $phpDateObject = new \DateTime('1900-01-01 ' . $hour . ':' . $minute . ':' . $second);
+
+        return $phpDateObject;
     }
 
     /**
@@ -462,6 +411,8 @@ public static function TIME($hour = 0, $minute = 0, $second = 0)
      */
     public static function DATEVALUE($dateValue = 1)
     {
+        $dti = new DateTimeImmutable();
+        $baseYear = Date::getExcelCalendar();
         $dateValue = trim(Functions::flattenSingleValue($dateValue), '"');
         //    Strip any ordinals because they're allowed in Excel (English only)
         $dateValue = preg_replace('/(\d)(st|nd|rd|th)([ -\/])/Ui', '$1$3', $dateValue);
@@ -470,6 +421,7 @@ public static function DATEVALUE($dateValue = 1)
 
         $yearFound = false;
         $t1 = explode(' ', $dateValue);
+        $t = '';
         foreach ($t1 as &$t) {
             if ((is_numeric($t)) && ($t > 31)) {
                 if ($yearFound) {
@@ -481,10 +433,11 @@ public static function DATEVALUE($dateValue = 1)
                 $yearFound = true;
             }
         }
-        if ((count($t1) == 1) && (strpos($t, ':') !== false)) {
+        if (count($t1) === 1) {
             //    We've been fed a time value without any date
-            return 0.0;
-        } elseif (count($t1) == 2) {
+            return ((strpos($t, ':') === false)) ? Functions::Value() : 0.0;
+        }
+        if (count($t1) == 2) {
             //    We only have two parts of the date: either day/month or month/year
             if ($yearFound) {
                 array_unshift($t1, 1);
@@ -493,7 +446,7 @@ public static function DATEVALUE($dateValue = 1)
                     $t1[1] += 1900;
                     array_unshift($t1, 1);
                 } else {
-                    $t1[] = date('Y');
+                    $t1[] = $dti->format('Y');
                 }
             }
         }
@@ -502,23 +455,13 @@ public static function DATEVALUE($dateValue = 1)
 
         $PHPDateArray = date_parse($dateValue);
         if (($PHPDateArray === false) || ($PHPDateArray['error_count'] > 0)) {
+            // If original count was 1, we've already returned.
+            // If it was 2, we added another.
+            // Therefore, neither of the first 2 stroks below can fail.
             $testVal1 = strtok($dateValue, '- ');
-            if ($testVal1 !== false) {
-                $testVal2 = strtok('- ');
-                if ($testVal2 !== false) {
-                    $testVal3 = strtok('- ');
-                    if ($testVal3 === false) {
-                        $testVal3 = strftime('%Y');
-                    }
-                } else {
-                    return Functions::VALUE();
-                }
-            } else {
-                return Functions::VALUE();
-            }
-            if ($testVal1 < 31 && $testVal2 < 12 && $testVal3 < 12 && strlen($testVal3) == 2) {
-                $testVal3 += 2000;
-            }
+            $testVal2 = strtok('- ');
+            $testVal3 = strtok('- ') ?: $dti->format('Y');
+            self::adjustYear($testVal1, $testVal2, $testVal3);
             $PHPDateArray = date_parse($testVal1 . '-' . $testVal2 . '-' . $testVal3);
             if (($PHPDateArray === false) || ($PHPDateArray['error_count'] > 0)) {
                 $PHPDateArray = date_parse($testVal2 . '-' . $testVal1 . '-' . $testVal3);
@@ -528,44 +471,126 @@ public static function DATEVALUE($dateValue = 1)
             }
         }
 
+        $retValue = Functions::Value();
         if (($PHPDateArray !== false) && ($PHPDateArray['error_count'] == 0)) {
             // Execute function
-            if ($PHPDateArray['year'] == '') {
-                $PHPDateArray['year'] = strftime('%Y');
-            }
-            if ($PHPDateArray['year'] < 1900) {
+            self::replaceIfEmpty($PHPDateArray['year'], $dti->format('Y'));
+            if ($PHPDateArray['year'] < $baseYear) {
                 return Functions::VALUE();
             }
-            if ($PHPDateArray['month'] == '') {
-                $PHPDateArray['month'] = strftime('%m');
-            }
-            if ($PHPDateArray['day'] == '') {
-                $PHPDateArray['day'] = strftime('%d');
+            self::replaceIfEmpty($PHPDateArray['month'], $dti->format('m'));
+            self::replaceIfEmpty($PHPDateArray['day'], $dti->format('d'));
+            $PHPDateArray['hour'] = 0;
+            $PHPDateArray['minute'] = 0;
+            $PHPDateArray['second'] = 0;
+            $month = (int) $PHPDateArray['month'];
+            $day = (int) $PHPDateArray['day'];
+            $year = (int) $PHPDateArray['year'];
+            if (!checkdate($month, $day, $year)) {
+                return ($year === 1900 && $month === 2 && $day === 29) ? self::returnIn3FormatsFloat(60.0) : Functions::VALUE();
             }
-            if (!checkdate($PHPDateArray['month'], $PHPDateArray['day'], $PHPDateArray['year'])) {
-                return Functions::VALUE();
+            $retValue = is_array($PHPDateArray) ? self::returnIn3FormatsArray($PHPDateArray, true) : Functions::VALUE();
+        }
+
+        return $retValue;
+    }
+
+    /**
+     * Help reduce perceived complexity of some tests.
+     *
+     * @param mixed $value
+     * @param mixed $altValue
+     */
+    private static function replaceIfEmpty(&$value, $altValue): void
+    {
+        $value = $value ?: $altValue;
+    }
+
+    /**
+     * Adjust year in ambiguous situations.
+     */
+    private static function adjustYear(string $testVal1, string $testVal2, string &$testVal3): void
+    {
+        if (!is_numeric($testVal1) || $testVal1 < 31) {
+            if (!is_numeric($testVal2) || $testVal2 < 12) {
+                if (is_numeric($testVal3) && $testVal3 < 12) {
+                    $testVal3 += 2000;
+                }
             }
-            $excelDateValue = floor(
-                Date::formattedPHPToExcel(
-                    $PHPDateArray['year'],
-                    $PHPDateArray['month'],
-                    $PHPDateArray['day'],
-                    $PHPDateArray['hour'],
-                    $PHPDateArray['minute'],
-                    $PHPDateArray['second']
-                )
+        }
+    }
+
+    /**
+     * Return result in one of three formats.
+     *
+     * @return mixed
+     */
+    private static function returnIn3FormatsArray(array $dateArray, bool $noFrac = false)
+    {
+        $retType = Functions::getReturnDateType();
+        if ($retType === Functions::RETURNDATE_PHP_DATETIME_OBJECT) {
+            return new \DateTime(
+                $dateArray['year']
+                . '-' . $dateArray['month']
+                . '-' . $dateArray['day']
+                . ' ' . $dateArray['hour']
+                . ':' . $dateArray['minute']
+                . ':' . $dateArray['second']
             );
-            switch (Functions::getReturnDateType()) {
-                case Functions::RETURNDATE_EXCEL:
-                    return (float) $excelDateValue;
-                case Functions::RETURNDATE_UNIX_TIMESTAMP:
-                    return (int) Date::excelToTimestamp($excelDateValue);
-                case Functions::RETURNDATE_PHP_DATETIME_OBJECT:
-                    return new \DateTime($PHPDateArray['year'] . '-' . $PHPDateArray['month'] . '-' . $PHPDateArray['day'] . ' 00:00:00');
-            }
         }
+        $excelDateValue =
+            Date::formattedPHPToExcel(
+                $dateArray['year'],
+                $dateArray['month'],
+                $dateArray['day'],
+                $dateArray['hour'],
+                $dateArray['minute'],
+                $dateArray['second']
+            );
+        if ($retType === Functions::RETURNDATE_EXCEL) {
+            return $noFrac ? floor($excelDateValue) : (float) $excelDateValue;
+        }
+        // RETURNDATE_UNIX_TIMESTAMP)
 
-        return Functions::VALUE();
+        return (int) Date::excelToTimestamp($excelDateValue);
+    }
+
+    /**
+     * Return result in one of three formats.
+     *
+     * @return mixed
+     */
+    private static function returnIn3FormatsFloat(float $excelDateValue)
+    {
+        $retType = Functions::getReturnDateType();
+        if ($retType === Functions::RETURNDATE_EXCEL) {
+            return $excelDateValue;
+        }
+        if ($retType === Functions::RETURNDATE_UNIX_TIMESTAMP) {
+            return (int) Date::excelToTimestamp($excelDateValue);
+        }
+        // RETURNDATE_PHP_DATETIME_OBJECT
+
+        return Date::excelToDateTimeObject($excelDateValue);
+    }
+
+    /**
+     * Return result in one of three formats.
+     *
+     * @return mixed
+     */
+    private static function returnIn3FormatsObject(\DateTime $PHPDateObject)
+    {
+        $retType = Functions::getReturnDateType();
+        if ($retType === Functions::RETURNDATE_PHP_DATETIME_OBJECT) {
+            return $PHPDateObject;
+        }
+        if ($retType === Functions::RETURNDATE_EXCEL) {
+            return (float) Date::PHPToExcel($PHPDateObject);
+        }
+        // RETURNDATE_UNIX_TIMESTAMP
+
+        return (int) Date::excelToTimestamp(Date::PHPToExcel($PHPDateObject));
     }
 
     /**
@@ -601,31 +626,22 @@ public static function TIMEVALUE($timeValue)
         }
 
         $PHPDateArray = date_parse($timeValue);
+        $retValue = Functions::VALUE();
         if (($PHPDateArray !== false) && ($PHPDateArray['error_count'] == 0)) {
-            if (Functions::getCompatibilityMode() == Functions::COMPATIBILITY_OPENOFFICE) {
-                $excelDateValue = Date::formattedPHPToExcel(
-                    $PHPDateArray['year'],
-                    $PHPDateArray['month'],
-                    $PHPDateArray['day'],
-                    $PHPDateArray['hour'],
-                    $PHPDateArray['minute'],
-                    $PHPDateArray['second']
-                );
+            // OpenOffice-specific code removed - it works just like Excel
+            $excelDateValue = Date::formattedPHPToExcel(1900, 1, 1, $PHPDateArray['hour'], $PHPDateArray['minute'], $PHPDateArray['second']) - 1;
+
+            $retType = Functions::getReturnDateType();
+            if ($retType === Functions::RETURNDATE_EXCEL) {
+                $retValue = (float) $excelDateValue;
+            } elseif ($retType === Functions::RETURNDATE_UNIX_TIMESTAMP) {
+                $retValue = (int) $phpDateValue = Date::excelToTimestamp($excelDateValue + 25569) - 3600;
             } else {
-                $excelDateValue = Date::formattedPHPToExcel(1900, 1, 1, $PHPDateArray['hour'], $PHPDateArray['minute'], $PHPDateArray['second']) - 1;
-            }
-
-            switch (Functions::getReturnDateType()) {
-                case Functions::RETURNDATE_EXCEL:
-                    return (float) $excelDateValue;
-                case Functions::RETURNDATE_UNIX_TIMESTAMP:
-                    return (int) $phpDateValue = Date::excelToTimestamp($excelDateValue + 25569) - 3600;
-                case Functions::RETURNDATE_PHP_DATETIME_OBJECT:
-                    return new \DateTime('1900-01-01 ' . $PHPDateArray['hour'] . ':' . $PHPDateArray['minute'] . ':' . $PHPDateArray['second']);
+                $retValue = new \DateTime('1900-01-01 ' . $PHPDateArray['hour'] . ':' . $PHPDateArray['minute'] . ':' . $PHPDateArray['second']);
             }
         }
 
-        return Functions::VALUE();
+        return $retValue;
     }
 
     /**
@@ -980,7 +996,7 @@ public static function NETWORKDAYS($startDate, $endDate, ...$dateArgs)
         // Execute function
         $startDoW = 6 - self::WEEKDAY($startDate, 2);
         if ($startDoW < 0) {
-            $startDoW = 0;
+            $startDoW = 5;
         }
         $endDoW = self::WEEKDAY($endDate, 2);
         if ($endDoW >= 6) {
@@ -1113,14 +1129,7 @@ public static function WORKDAY($startDate, $endDays, ...$dateArgs)
             }
         }
 
-        switch (Functions::getReturnDateType()) {
-            case Functions::RETURNDATE_EXCEL:
-                return (float) $endDate;
-            case Functions::RETURNDATE_UNIX_TIMESTAMP:
-                return (int) Date::excelToTimestamp($endDate);
-            case Functions::RETURNDATE_PHP_DATETIME_OBJECT:
-                return Date::excelToDateTimeObject($endDate);
-        }
+        return self::returnIn3FormatsFloat($endDate);
     }
 
     /**
@@ -1141,9 +1150,10 @@ public static function DAYOFMONTH($dateValue = 1)
     {
         $dateValue = Functions::flattenSingleValue($dateValue);
 
-        if ($dateValue === null) {
-            $dateValue = 1;
-        } elseif (is_string($dateValue = self::getDateValue($dateValue))) {
+        if ($dateValue === null || is_bool($dateValue)) {
+            return (int) $dateValue;
+        }
+        if (is_string($dateValue = self::getDateValue($dateValue))) {
             return Functions::VALUE();
         }
 
@@ -1170,7 +1180,7 @@ public static function DAYOFMONTH($dateValue = 1)
      * Excel Function:
      *        WEEKDAY(dateValue[,style])
      *
-     * @param int $dateValue Excel date serial value (float), PHP date timestamp (integer),
+     * @param float|int|string $dateValue Excel date serial value (float), PHP date timestamp (integer),
      *                                    PHP DateTime object, or a standard date string
      * @param int $style A number that determines the type of return value
      *                                        1 or omitted    Numbers 1 (Sunday) through 7 (Saturday).
@@ -1182,6 +1192,7 @@ public static function DAYOFMONTH($dateValue = 1)
     public static function WEEKDAY($dateValue = 1, $style = 1)
     {
         $dateValue = Functions::flattenSingleValue($dateValue);
+        self::nullFalseTrueToNumber($dateValue);
         $style = Functions::flattenSingleValue($style);
 
         if (!is_numeric($style)) {
@@ -1191,19 +1202,19 @@ public static function WEEKDAY($dateValue = 1, $style = 1)
         }
         $style = floor($style);
 
-        if ($dateValue === null) {
-            $dateValue = 1;
-        } elseif (is_string($dateValue = self::getDateValue($dateValue))) {
+        $dateValue = self::getDateValue($dateValue);
+        if (is_string($dateValue)) {
             return Functions::VALUE();
-        } elseif ($dateValue < 0.0) {
+        }
+        if ($dateValue < 0.0) {
             return Functions::NAN();
         }
 
         // Execute function
         $PHPDateObject = Date::excelToDateTimeObject($dateValue);
+        self::silly1900($PHPDateObject);
         $DoW = (int) $PHPDateObject->format('w');
 
-        $firstDay = 1;
         switch ($style) {
             case 1:
                 ++$DoW;
@@ -1219,20 +1230,10 @@ public static function WEEKDAY($dateValue = 1, $style = 1)
                 if ($DoW === 0) {
                     $DoW = 7;
                 }
-                $firstDay = 0;
                 --$DoW;
 
                 break;
         }
-        if (Functions::getCompatibilityMode() == Functions::COMPATIBILITY_EXCEL) {
-            //    Test for Excel's 1900 leap year, and introduce the error as required
-            if (($PHPDateObject->format('Y') == 1900) && ($PHPDateObject->format('n') <= 2)) {
-                --$DoW;
-                if ($DoW < $firstDay) {
-                    $DoW += 7;
-                }
-            }
-        }
 
         return $DoW;
     }
@@ -1298,17 +1299,26 @@ public static function WEEKDAY($dateValue = 1, $style = 1)
      */
     public static function WEEKNUM($dateValue = 1, $method = self::STARTWEEK_SUNDAY)
     {
+        $origDateValueNull = $dateValue === null;
         $dateValue = Functions::flattenSingleValue($dateValue);
         $method = Functions::flattenSingleValue($method);
-
         if (!is_numeric($method)) {
             return Functions::VALUE();
         }
+
         $method = (int) $method;
         if (!array_key_exists($method, self::METHODARR)) {
             return Functions::NaN();
         }
         $method = self::METHODARR[$method];
+        if ($dateValue === null) { // boolean not allowed
+            // This seems to be an additional Excel bug.
+            if (self::buggyWeekNum1900($method)) {
+                return 0;
+            }
+            //$dateValue = 1;
+            $dateValue = (Date::getExcelCalendar() === DATE::CALENDAR_MAC_1904) ? 0 : 1;
+        }
 
         $dateValue = self::getDateValue($dateValue);
         if (is_string($dateValue)) {
@@ -1321,8 +1331,14 @@ public static function WEEKNUM($dateValue = 1, $method = self::STARTWEEK_SUNDAY)
         // Execute function
         $PHPDateObject = Date::excelToDateTimeObject($dateValue);
         if ($method == self::STARTWEEK_MONDAY_ISO) {
+            self::silly1900($PHPDateObject);
+
             return (int) $PHPDateObject->format('W');
         }
+        if (self::buggyWeekNum1904($method, $origDateValueNull, $PHPDateObject)) {
+            return 0;
+        }
+        self::silly1900($PHPDateObject, '+ 5 years'); // 1905 calendar matches
         $dayOfYear = $PHPDateObject->format('z');
         $PHPDateObject->modify('-' . $dayOfYear . ' days');
         $firstDayOfFirstWeek = $PHPDateObject->format('w');
@@ -1334,6 +1350,18 @@ public static function WEEKNUM($dateValue = 1, $method = self::STARTWEEK_SUNDAY)
         return (int) $weekOfYear;
     }
 
+    private static function buggyWeekNum1900(int $method): bool
+    {
+        return $method === self::DOW_SUNDAY && Date::getExcelCalendar() === Date::CALENDAR_WINDOWS_1900;
+    }
+
+    private static function buggyWeekNum1904(int $method, bool $origNull, \DateTime $dateObject): bool
+    {
+        // This appears to be another Excel bug.
+
+        return $method === self::DOW_SUNDAY && Date::getExcelCalendar() === Date::CALENDAR_MAC_1904 && !$origNull && $dateObject->format('Y-m-d') === '1904-01-01';
+    }
+
     /**
      * ISOWEEKNUM.
      *
@@ -1350,17 +1378,19 @@ public static function WEEKNUM($dateValue = 1, $method = self::STARTWEEK_SUNDAY)
     public static function ISOWEEKNUM($dateValue = 1)
     {
         $dateValue = Functions::flattenSingleValue($dateValue);
+        self::nullFalseTrueToNumber($dateValue);
 
-        if ($dateValue === null) {
-            $dateValue = 1;
-        } elseif (is_string($dateValue = self::getDateValue($dateValue))) {
+        $dateValue = self::getDateValue($dateValue);
+        if (!is_numeric($dateValue)) {
             return Functions::VALUE();
-        } elseif ($dateValue < 0.0) {
+        }
+        if ($dateValue < 0.0) {
             return Functions::NAN();
         }
 
         // Execute function
         $PHPDateObject = Date::excelToDateTimeObject($dateValue);
+        self::silly1900($PHPDateObject);
 
         return (int) $PHPDateObject->format('W');
     }
@@ -1449,12 +1479,7 @@ public static function HOUROFDAY($timeValue = 0)
         $timeValue = Functions::flattenSingleValue($timeValue);
 
         if (!is_numeric($timeValue)) {
-            if (Functions::getCompatibilityMode() == Functions::COMPATIBILITY_GNUMERIC) {
-                $testVal = strtok($timeValue, '/-: ');
-                if (strlen($testVal) < strlen($timeValue)) {
-                    return Functions::VALUE();
-                }
-            }
+            // Gnumeric test removed - it operates like Excel
             $timeValue = self::getTimeValue($timeValue);
             if (is_string($timeValue)) {
                 return Functions::VALUE();
@@ -1490,12 +1515,7 @@ public static function MINUTE($timeValue = 0)
         $timeValue = $timeTester = Functions::flattenSingleValue($timeValue);
 
         if (!is_numeric($timeValue)) {
-            if (Functions::getCompatibilityMode() == Functions::COMPATIBILITY_GNUMERIC) {
-                $testVal = strtok($timeValue, '/-: ');
-                if (strlen($testVal) < strlen($timeValue)) {
-                    return Functions::VALUE();
-                }
-            }
+            // Gnumeric test removed - it operates like Excel
             $timeValue = self::getTimeValue($timeValue);
             if (is_string($timeValue)) {
                 return Functions::VALUE();
@@ -1531,12 +1551,7 @@ public static function SECOND($timeValue = 0)
         $timeValue = Functions::flattenSingleValue($timeValue);
 
         if (!is_numeric($timeValue)) {
-            if (Functions::getCompatibilityMode() == Functions::COMPATIBILITY_GNUMERIC) {
-                $testVal = strtok($timeValue, '/-: ');
-                if (strlen($testVal) < strlen($timeValue)) {
-                    return Functions::VALUE();
-                }
-            }
+            // Gnumeric test removed - it operates like Excel
             $timeValue = self::getTimeValue($timeValue);
             if (is_string($timeValue)) {
                 return Functions::VALUE();
@@ -1590,14 +1605,7 @@ public static function EDATE($dateValue = 1, $adjustmentMonths = 0)
         // Execute function
         $PHPDateObject = self::adjustDateByMonths($dateValue, $adjustmentMonths);
 
-        switch (Functions::getReturnDateType()) {
-            case Functions::RETURNDATE_EXCEL:
-                return (float) Date::PHPToExcel($PHPDateObject);
-            case Functions::RETURNDATE_UNIX_TIMESTAMP:
-                return (int) Date::excelToTimestamp(Date::PHPToExcel($PHPDateObject));
-            case Functions::RETURNDATE_PHP_DATETIME_OBJECT:
-                return $PHPDateObject;
-        }
+        return self::returnIn3FormatsObject($PHPDateObject);
     }
 
     /**
@@ -1639,13 +1647,31 @@ public static function EOMONTH($dateValue = 1, $adjustmentMonths = 0)
         $adjustDaysString = '-' . $adjustDays . ' days';
         $PHPDateObject->modify($adjustDaysString);
 
-        switch (Functions::getReturnDateType()) {
-            case Functions::RETURNDATE_EXCEL:
-                return (float) Date::PHPToExcel($PHPDateObject);
-            case Functions::RETURNDATE_UNIX_TIMESTAMP:
-                return (int) Date::excelToTimestamp(Date::PHPToExcel($PHPDateObject));
-            case Functions::RETURNDATE_PHP_DATETIME_OBJECT:
-                return $PHPDateObject;
+        return self::returnIn3FormatsObject($PHPDateObject);
+    }
+
+    /**
+     * Many functions accept null/false/true argument treated as 0/0/1.
+     *
+     * @param mixed $number
+     */
+    private static function nullFalseTrueToNumber(&$number): void
+    {
+        $number = Functions::flattenSingleValue($number);
+        $baseYear = Date::getExcelCalendar();
+        $nullVal = $baseYear === DATE::CALENDAR_MAC_1904 ? 0 : 1;
+        if ($number === null) {
+            $number = $nullVal;
+        } elseif (is_bool($number)) {
+            $number = $nullVal + (int) $number;
+        }
+    }
+
+    private static function silly1900(\DateTime $PHPDateObject, string $mod = '-1 day'): void
+    {
+        $isoDate = $PHPDateObject->format('c');
+        if ($isoDate < '1900-03-01') {
+            $PHPDateObject->modify($mod);
         }
     }
 }
diff --git a/src/PhpSpreadsheet/Shared/Date.php b/src/PhpSpreadsheet/Shared/Date.php
index 180a71596d..28c39255e4 100644
--- a/src/PhpSpreadsheet/Shared/Date.php
+++ b/src/PhpSpreadsheet/Shared/Date.php
@@ -160,7 +160,7 @@ public static function excelToDateTimeObject($excelTimestamp, $timeZone = null)
     {
         $timeZone = ($timeZone === null) ? self::getDefaultTimezone() : self::validateTimeZone($timeZone);
         if (Functions::getCompatibilityMode() == Functions::COMPATIBILITY_EXCEL) {
-            if ($excelTimestamp < 1.0) {
+            if ($excelTimestamp < 1 && self::$excelCalendar === self::CALENDAR_WINDOWS_1900) {
                 // Unix timestamp base date
                 $baseDate = new \DateTime('1970-01-01', $timeZone);
             } else {
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DateTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DateTest.php
index 48f7cfd7ec..aad59729be 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DateTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DateTest.php
@@ -9,11 +9,21 @@
 
 class DateTest extends TestCase
 {
+    private $returnDateType;
+
+    private $excelCalendar;
+
     protected function setUp(): void
     {
-        Functions::setCompatibilityMode(Functions::COMPATIBILITY_EXCEL);
+        $this->returnDateType = Functions::getReturnDateType();
+        $this->excelCalendar = Date::getExcelCalendar();
         Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
-        Date::setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
+    }
+
+    protected function tearDown(): void
+    {
+        Functions::setReturnDateType($this->returnDateType);
+        Date::setExcelCalendar($this->excelCalendar);
     }
 
     /**
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DateValueTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DateValueTest.php
index 51e4f7c0cf..72e036f95d 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DateValueTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DateValueTest.php
@@ -2,6 +2,7 @@
 
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
+use DateTimeImmutable;
 use DateTimeInterface;
 use PhpOffice\PhpSpreadsheet\Calculation\DateTime;
 use PhpOffice\PhpSpreadsheet\Calculation\Functions;
@@ -10,11 +11,21 @@
 
 class DateValueTest extends TestCase
 {
+    private $returnDateType;
+
+    private $excelCalendar;
+
     protected function setUp(): void
     {
-        Functions::setCompatibilityMode(Functions::COMPATIBILITY_EXCEL);
+        $this->returnDateType = Functions::getReturnDateType();
+        $this->excelCalendar = Date::getExcelCalendar();
         Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
-        Date::setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
+    }
+
+    protected function tearDown(): void
+    {
+        Functions::setReturnDateType($this->returnDateType);
+        Date::setExcelCalendar($this->excelCalendar);
     }
 
     /**
@@ -25,7 +36,21 @@ protected function setUp(): void
      */
     public function testDATEVALUE($expectedResult, $dateValue): void
     {
-        $result = DateTime::DATEVALUE($dateValue);
+        // Loop to avoid extraordinarily rare edge case where first calculation
+        // and second do not take place on same day.
+        do {
+            $dtStart = new DateTimeImmutable();
+            $startDay = $dtStart->format('d');
+            if (is_string($expectedResult)) {
+                $replYMD = str_replace('Y', date('Y'), $expectedResult);
+                if ($replYMD !== $expectedResult) {
+                    $expectedResult = DateTime::DATEVALUE($replYMD);
+                }
+            }
+            $result = DateTime::DATEVALUE($dateValue);
+            $dtEnd = new DateTimeImmutable();
+            $endDay = $dtEnd->format('d');
+        } while ($startDay !== $endDay);
         self::assertEqualsWithDelta($expectedResult, $result, 1E-8);
     }
 
@@ -55,4 +80,13 @@ public function testDATEVALUEtoDateTimeObject(): void
         //    ... with the correct value
         self::assertEquals($result->format('d-M-Y'), '31-Jan-2012');
     }
+
+    public function testDATEVALUEwith1904Calendar(): void
+    {
+        Date::setExcelCalendar(Date::CALENDAR_MAC_1904);
+        self::assertEquals(5428, DateTime::DATEVALUE('1918-11-11'));
+        self::assertEquals(0, DateTime::DATEVALUE('1904-01-01'));
+        self::assertEquals('#VALUE!', DateTime::DATEVALUE('1903-12-31'));
+        self::assertEquals('#VALUE!', DateTime::DATEVALUE('1900-02-29'));
+    }
 }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/NowTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/NowTest.php
new file mode 100644
index 0000000000..f139f70393
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/NowTest.php
@@ -0,0 +1,38 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
+
+use DateTimeImmutable;
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+use PHPUnit\Framework\TestCase;
+
+class NowTest extends TestCase
+{
+    public function testNow(): void
+    {
+        $spreadsheet = new Spreadsheet();
+        $sheet = $spreadsheet->getActiveSheet();
+        // Loop to avoid rare edge case where first calculation
+        // and second do not take place in same second.
+        do {
+            $dtStart = new DateTimeImmutable();
+            $startSecond = $dtStart->format('s');
+            $sheet->setCellValue('A1', '=NOW()');
+            $dtEnd = new DateTimeImmutable();
+            $endSecond = $dtEnd->format('s');
+        } while ($startSecond !== $endSecond);
+        //echo("\n"); var_dump($sheet->getCell('A1')->getCalculatedValue()); echo ("\n");
+        $sheet->setCellValue('B1', '=YEAR(A1)');
+        $sheet->setCellValue('C1', '=MONTH(A1)');
+        $sheet->setCellValue('D1', '=DAY(A1)');
+        $sheet->setCellValue('E1', '=HOUR(A1)');
+        $sheet->setCellValue('F1', '=MINUTE(A1)');
+        $sheet->setCellValue('G1', '=SECOND(A1)');
+        self::assertEquals($dtStart->format('Y'), $sheet->getCell('B1')->getCalculatedValue());
+        self::assertEquals($dtStart->format('m'), $sheet->getCell('C1')->getCalculatedValue());
+        self::assertEquals($dtStart->format('d'), $sheet->getCell('D1')->getCalculatedValue());
+        self::assertEquals($dtStart->format('H'), $sheet->getCell('E1')->getCalculatedValue());
+        self::assertEquals($dtStart->format('i'), $sheet->getCell('F1')->getCalculatedValue());
+        self::assertEquals($dtStart->format('s'), $sheet->getCell('G1')->getCalculatedValue());
+    }
+}
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/TimeTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/TimeTest.php
index 344061d48b..3ef58374a6 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/TimeTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/TimeTest.php
@@ -9,11 +9,20 @@
 
 class TimeTest extends TestCase
 {
+    private $returnDateType;
+
+    private $calendar;
+
     protected function setUp(): void
     {
-        Functions::setCompatibilityMode(Functions::COMPATIBILITY_EXCEL);
-        Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
-        Date::setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
+        $this->returnDateType = Functions::getReturnDateType();
+        $this->calendar = Date::getExcelCalendar();
+    }
+
+    protected function tearDown(): void
+    {
+        Functions::setReturnDateType($this->returnDateType);
+        Date::setExcelCalendar($this->calendar);
     }
 
     /**
@@ -23,6 +32,7 @@ protected function setUp(): void
      */
     public function testTIME($expectedResult, ...$args): void
     {
+        Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
         $result = DateTime::TIME(...$args);
         self::assertEqualsWithDelta($expectedResult, $result, 1E-8);
     }
@@ -52,4 +62,20 @@ public function testTIMEtoDateTimeObject(): void
         //    ... with the correct value
         self::assertEquals($result->format('H:i:s'), '07:30:20');
     }
+
+    public function testTIME1904(): void
+    {
+        Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
+        Date::setExcelCalendar(Date::CALENDAR_MAC_1904);
+        $result = DateTime::TIME(0, 0, 0);
+        self::assertEquals(0, $result);
+    }
+
+    public function testTIME1900(): void
+    {
+        Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
+        Date::setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
+        $result = DateTime::TIME(0, 0, 0);
+        self::assertEquals(0, $result);
+    }
 }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekDayTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekDayTest.php
index c5b89e01e1..99aa6f7cb9 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekDayTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekDayTest.php
@@ -3,17 +3,21 @@
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use PhpOffice\PhpSpreadsheet\Calculation\DateTime;
-use PhpOffice\PhpSpreadsheet\Calculation\Functions;
 use PhpOffice\PhpSpreadsheet\Shared\Date;
 use PHPUnit\Framework\TestCase;
 
 class WeekDayTest extends TestCase
 {
+    private $excelCalendar;
+
     protected function setUp(): void
     {
-        Functions::setCompatibilityMode(Functions::COMPATIBILITY_EXCEL);
-        Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
-        Date::setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
+        $this->excelCalendar = Date::getExcelCalendar();
+    }
+
+    protected function tearDown(): void
+    {
+        Date::setExcelCalendar($this->excelCalendar);
     }
 
     /**
@@ -31,4 +35,12 @@ public function providerWEEKDAY()
     {
         return require 'tests/data/Calculation/DateTime/WEEKDAY.php';
     }
+
+    public function testWEEKDAYwith1904Calendar(): void
+    {
+        Date::setExcelCalendar(Date::CALENDAR_MAC_1904);
+        self::assertEquals(7, DateTime::WEEKDAY('1904-01-02'));
+        self::assertEquals(6, DateTime::WEEKDAY('1904-01-01'));
+        self::assertEquals(6, DateTime::WEEKDAY(null));
+    }
 }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekNumTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekNumTest.php
index 9d8e1eb281..17119f2873 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekNumTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekNumTest.php
@@ -3,17 +3,21 @@
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use PhpOffice\PhpSpreadsheet\Calculation\DateTime;
-use PhpOffice\PhpSpreadsheet\Calculation\Functions;
 use PhpOffice\PhpSpreadsheet\Shared\Date;
 use PHPUnit\Framework\TestCase;
 
 class WeekNumTest extends TestCase
 {
+    private $excelCalendar;
+
     protected function setUp(): void
     {
-        Functions::setCompatibilityMode(Functions::COMPATIBILITY_EXCEL);
-        Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
-        Date::setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
+        $this->excelCalendar = Date::getExcelCalendar();
+    }
+
+    protected function tearDown(): void
+    {
+        Date::setExcelCalendar($this->excelCalendar);
     }
 
     /**
@@ -31,4 +35,14 @@ public function providerWEEKNUM()
     {
         return require 'tests/data/Calculation/DateTime/WEEKNUM.php';
     }
+
+    public function testWEEKNUMwith1904Calendar(): void
+    {
+        Date::setExcelCalendar(Date::CALENDAR_MAC_1904);
+        self::assertEquals(27, DateTime::WEEKNUM('2004-07-02'));
+        self::assertEquals(1, DateTime::WEEKNUM('1904-01-02'));
+        self::assertEquals(1, DateTime::WEEKNUM(null));
+        // The following is a bug in Excel.
+        self::assertEquals(0, DateTime::WEEKNUM('1904-01-01'));
+    }
 }
diff --git a/tests/PhpSpreadsheetTests/Reader/Ods/OdsTest.php b/tests/PhpSpreadsheetTests/Reader/Ods/OdsTest.php
index 8be1aa7cc1..0160f68d62 100644
--- a/tests/PhpSpreadsheetTests/Reader/Ods/OdsTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Ods/OdsTest.php
@@ -15,6 +15,19 @@
  */
 class OdsTest extends TestCase
 {
+    private $timeZone;
+
+    protected function setUp(): void
+    {
+        $this->timeZone = date_default_timezone_get();
+        date_default_timezone_set('UTC');
+    }
+
+    protected function tearDown(): void
+    {
+        date_default_timezone_set($this->timeZone);
+    }
+
     /**
      * @var Spreadsheet
      */
@@ -153,13 +166,13 @@ public function testReadValueAndComments(): void
         self::assertEquals(0, $firstSheet->getCell('G10')->getValue());
 
         self::assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('A10')->getDataType()); // Date
-        self::assertEquals(22269.0, $firstSheet->getCell('A10')->getValue());
+        self::assertEquals('19-Dec-60', $firstSheet->getCell('A10')->getFormattedValue());
 
         self::assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('A13')->getDataType()); // Time
-        self::assertEquals(25569.0625, $firstSheet->getCell('A13')->getValue());
+        self::assertEquals('2:30:00', $firstSheet->getCell('A13')->getFormattedValue());
 
         self::assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('A15')->getDataType()); // Date + Time
-        self::assertEquals(22269.0625, $firstSheet->getCell('A15')->getValue());
+        self::assertEquals('19-Dec-60 1:30:00', $firstSheet->getCell('A15')->getFormattedValue());
 
         self::assertEquals(DataType::TYPE_NUMERIC, $firstSheet->getCell('A11')->getDataType()); // Fraction
 
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index 77cd522838..9ebd3f2623 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -3,4 +3,4 @@
 setlocale(LC_ALL, 'en_US.utf8');
 
 // PHP 5.3 Compat
-date_default_timezone_set('Europe/London');
+//date_default_timezone_set('Europe/London');
diff --git a/tests/data/Calculation/DateTime/DATEVALUE.php b/tests/data/Calculation/DateTime/DATEVALUE.php
index 17110c749b..0b0f110f5e 100644
--- a/tests/data/Calculation/DateTime/DATEVALUE.php
+++ b/tests/data/Calculation/DateTime/DATEVALUE.php
@@ -20,12 +20,12 @@
         '1900/2/28',
     ],
     [
-        '#VALUE!',
+        '60',
         '29-02-1900',
     ],
     // MS Excel will fail with a #VALUE return, but PhpSpreadsheet can parse this date
     [
-        '#VALUE!',
+        '60',
         '29th February 1900',
     ],
     [
@@ -159,30 +159,32 @@
         '#VALUE!',
         'The 1st day of March 2007',
     ],
-    // 01/01 of the current year
+    // Jan 1 of the current year
     [
-        44197,
+        'Y-01-01',
         '1 Jan',
     ],
-    // 31/12 of the current year
+    // Dec 31 of the current year
     [
-        44561,
+        'Y-12-31',
         '31/12',
     ],
-    // Excel reads as 1st December 1931, not 31st December in current year
+    // Excel reads as 1st December 1931, not 31st December in current year.
+    // This result is locale-dependent in Excel, in a manner not
+    // supported by PhpSpreadsheet.
     [
         11658,
         '12/31',
     ],
-    // 05/07 of the current year
+    // July 5 of the current year
     [
-        44382,
+        'Y-07-05',
         '5-JUL',
     ],
-    // 05/07 of the current year
+    // July 5 of the current year
     [
-        44382,
-        '5 Jul',
+        'Y-07-05',
+        '5 July',
     ],
     [
         39783,
@@ -216,6 +218,11 @@
         '#VALUE!',
         12,
     ],
+    // implicit day of month is 1
+    [
+        40210,
+        'Feb-2010',
+    ],
     [
         40221,
         '12-Feb-2010',
@@ -294,4 +301,16 @@
         '#VALUE!',
         'ABCDEFGHIJKMNOPQRSTUVWXYZ',
     ],
+    [
+        '#VALUE!',
+        '1999',
+    ],
+    ['#VALUE!', '32/32'],
+    ['#VALUE!', '1910-'],
+    ['#VALUE!', '10--'],
+    ['#VALUE!', '--10'],
+    ['#VALUE!', '--1910'],
+    //['#VALUE!', '-JUL-1910'], We can parse this, Excel can't
+    ['#VALUE!', '2008-08-'],
+    [36751, '0-08-13'],
 ];
diff --git a/tests/data/Calculation/DateTime/DAY.php b/tests/data/Calculation/DateTime/DAY.php
index 8ba4ad41e8..81fab933b4 100644
--- a/tests/data/Calculation/DateTime/DAY.php
+++ b/tests/data/Calculation/DateTime/DAY.php
@@ -53,4 +53,19 @@
         30, // Result for OpenOffice
         0,
     ],
+    [
+        0, // Result for Excel
+        0, // Result for OpenOffice
+        null,
+    ],
+    [
+        1, // Result for Excel
+        1, // Result for OpenOffice
+        true,
+    ],
+    [
+        0, // Result for Excel
+        0, // Result for OpenOffice
+        false,
+    ],
 ];
diff --git a/tests/data/Calculation/DateTime/ISOWEEKNUM.php b/tests/data/Calculation/DateTime/ISOWEEKNUM.php
index 78a4d3e800..b6afd303e3 100644
--- a/tests/data/Calculation/DateTime/ISOWEEKNUM.php
+++ b/tests/data/Calculation/DateTime/ISOWEEKNUM.php
@@ -33,4 +33,14 @@
         '#VALUE!',
         '1800-01-01',
     ],
+    ['52', null],
+    ['53', '1904-01-01'],
+    ['52', '1900-01-01'],
+    ['1', '1900-01-07'],
+    ['1', '1900-01-08'],
+    ['2', '1900-01-09'],
+    ['9', '1900-03-04'],
+    ['10', '1900-03-05'],
+    ['#NUM!', '-1'],
+    [39, '1000'],
 ];
diff --git a/tests/data/Calculation/DateTime/NETWORKDAYS.php b/tests/data/Calculation/DateTime/NETWORKDAYS.php
index d62e501caf..db548ddc95 100644
--- a/tests/data/Calculation/DateTime/NETWORKDAYS.php
+++ b/tests/data/Calculation/DateTime/NETWORKDAYS.php
@@ -100,4 +100,22 @@
         '31-Jan-2007',
         '1-Feb-2007',
     ],
+    ['#VALUE!', 'ABQZ', '1-Feb-2007'],
+    ['#VALUE!', '1-Feb-2007', 'ABQZ'],
+    [10, '2021-02-13', '2021-02-27'],
+    [10, '2021-02-14', '2021-02-27'],
+    [3, '2021-02-14', '2021-02-17'],
+    [8, '2021-02-14', '2021-02-24'],
+    [9, '2021-02-14', '2021-02-25'],
+    [10, '2021-02-14', '2021-02-26'],
+    [9, '2021-02-13', '2021-02-25'],
+    [10, '2021-02-12', '2021-02-25'],
+    [
+        '#VALUE!',
+        '10-Jan-1961',
+        '19-Dec-1960',
+        '25-Dec-1960',
+        'ABQZ',
+        '01-Jan-1961',
+    ],
 ];
diff --git a/tests/data/Calculation/DateTime/WEEKDAY.php b/tests/data/Calculation/DateTime/WEEKDAY.php
index 8cc6808252..fadf11f72e 100644
--- a/tests/data/Calculation/DateTime/WEEKDAY.php
+++ b/tests/data/Calculation/DateTime/WEEKDAY.php
@@ -110,4 +110,11 @@
         '#NUM!',
         -1,
     ],
+    [1, null],
+    [1, false],
+    [2, true],
+    [1, '1900-01-01'],
+    [7, '1900-01-01', 2],
+    [7, null, 2],
+    [7, '1900-02-05', 2],
 ];
diff --git a/tests/data/Calculation/DateTime/WEEKNUM.php b/tests/data/Calculation/DateTime/WEEKNUM.php
index d73ee463ae..b109a5345f 100644
--- a/tests/data/Calculation/DateTime/WEEKNUM.php
+++ b/tests/data/Calculation/DateTime/WEEKNUM.php
@@ -173,4 +173,31 @@
         1,
         '2025-12-29', 21,
     ],
+    ['9', '1900-03-01'],
+    ['2', '1900-01-07', 2],
+    ['2', '1905-01-07', 2],
+    ['1', '1900-01-01'],
+    ['1', '1900-01-01', 2],
+    ['2', '1900-01-02', 2],
+    ['1', null, 11],
+    ['1', null, 12],
+    ['1', null, 13],
+    ['1', null, 14],
+    ['1', null, 15],
+    ['1', null, 16],
+    ['0', null, 17],
+    ['1', '1905-01-01', 17],
+    ['0', null],
+    ['1', null, 2],
+    ['1', '1906-01-01'],
+    ['#VALUE!', true],
+    ['#VALUE!', false, 21],
+    ['52', null, 21],
+    ['53', '1904-01-01', 21],
+    ['52', '1900-01-01', 21],
+    ['1', '1900-01-07', 21],
+    ['1', '1900-01-08', 21],
+    ['2', '1900-01-09', 21],
+    ['9', '1900-03-04', 21],
+    ['10', '1900-03-05', 21],
 ];
diff --git a/tests/data/Calculation/DateTime/WORKDAY.php b/tests/data/Calculation/DateTime/WORKDAY.php
index 76c517f952..fc5f648339 100644
--- a/tests/data/Calculation/DateTime/WORKDAY.php
+++ b/tests/data/Calculation/DateTime/WORKDAY.php
@@ -89,4 +89,20 @@
             ],
         ],
     ],
+    [
+        44242,
+        '15-Feb-2021',
+        0,
+    ],
+    [
+        '#VALUE!',
+        '5-Apr-2012',
+        3,
+        [
+            [
+                '6-Apr-2012',
+                'ABQZ',
+            ],
+        ],
+    ],
 ];
diff --git a/tests/data/Calculation/DateTime/YEARFRAC.php b/tests/data/Calculation/DateTime/YEARFRAC.php
index 3e76087c6b..abdb71d9eb 100644
--- a/tests/data/Calculation/DateTime/YEARFRAC.php
+++ b/tests/data/Calculation/DateTime/YEARFRAC.php
@@ -559,5 +559,6 @@
         '2025-05-28',
         1,
     ],
-
+    ['#VALUE!', '2023-04-27', 'ABQZ', 1],
+    ['#VALUE!', 'ABQZ', '2023-04-07', 1],
 ];
diff --git a/tests/data/Shared/Date/ExcelToTimestamp1904.php b/tests/data/Shared/Date/ExcelToTimestamp1904.php
index e0f3075435..1c013ab4ef 100644
--- a/tests/data/Shared/Date/ExcelToTimestamp1904.php
+++ b/tests/data/Shared/Date/ExcelToTimestamp1904.php
@@ -29,17 +29,17 @@
     ],
     // 06:00:00
     [
-        21600,
+        gmmktime(6, 0, 0, 1, 1, 1904), // 32-bit safe - no Y2038 problem
         0.25,
     ],
     // 08:00.00
     [
-        28800,
+        gmmktime(8, 0, 0, 1, 1, 1904), // 32-bit safe - no Y2038 problem
         0.3333333333333333333,
     ],
-    // 02:57:46
+    // 13:02:13
     [
-        46933,
+        gmmktime(13, 02, 13, 1, 1, 1904), // 32-bit safe - no Y2038 problem
         0.54321,
     ],
 ];