opensearch timestamp problem

[ghost]

Problem

when i use th plugin, i found the fileds inclueds timestamp,and it's utc time,the timestamp should be the same as _source timestamp

...

Steps to replicate

<source>
 @type tail
 path /var/log/cron
 pos_file /var/log/os/os2.log.pos
 read_from_head true
 tag syslog.cron
 <parse>
    @type json
  </parse>
</source>

<match syslog.cron.**>
  @type opensearch
  scheme https
  ssl_verify false
  hosts xxxx  # hosts
  user admin
  password admin
  index_name oslog-cronjob-%Y%m%d
  <buffer tag,time>
   timekey 60
   timekey_wait 0
   timekey_use_utc false
   timekey_zone +0800
  </buffer>
</match>

Expected Behavior or What you need to ask

i think the timestamp will be use the

timekey_zone +0800

but it's not work.
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Using Fluentd and OpenSearch plugin versions

• OS version
  • Linux version 4.18.0-305.el8.x86_64
  • td-agent 4.3.2 fluentd 1.14.6

2022-09-02 10:39:29 +0800 [info]: starting fluentd-1.15.0 pid=52989 ruby="2.7.6"
2022-09-02 10:39:29 +0800 [info]: spawn command to main:  cmdline=["/opt/td-agent/bin/ruby", "-Eascii-8bit:ascii-8bit", "/opt/td-agent/bin/fluentd", "--log", "/var/log/td-agent/td-agent.log", "--daemon", "/var/run/td-agent/td-agent.pid", "--under-supervisor"]                                                                    
2022-09-02 10:39:30 +0800 [info]: adding match pattern="syslog.cron.**" type="opensearch"                                                                          
2022-09-02 10:39:30 +0800 [info]: adding source type="tail"
2022-09-02 10:39:30 +0800 [info]: #0 starting fluentd worker pid=53031 ppid=53028 worker=0                                                                         
2022-09-02 10:39:30 +0800 [info]: #0 following tail of /var/log/cron
2022-09-02 10:39:30 +0800 [info]: #0 fluentd worker is now running worker=0