Fluentd wrong timestamp on out file

[hadrian08]

Hello,
Am playing around evaluating fluentd/fluent-bit; have the following setup: fluent-bit forwards some log data to fluentd for aggregation. Running on Windows Server 2019.
Have restarted fluentd on May 25 (it was initially started on 24 May):
...
2022-05-25 08:52:51 +0200 [info]: starting fluentd-1.14.6 pid=6748 ruby="2.7.6"
2022-05-25 08:52:51 +0200 [info]: spawn command to main: cmdline=["C:/opt/td-agent/bin/ruby.exe", "-Eascii-8bit:ascii-8bit", "C:/opt/td-agent/bin/fluentd", "-c", "fluentdNO_TLSReceiver.conf", "--under-supervisor"]
2022-05-25 08:52:54 +0200 [info]: adding source type="forward"
2022-05-25 08:52:54 +0200 [info]: #0 starting fluentd worker pid=15608 ppid=6748 worker=0
2022-05-25 08:52:54 +0200 [info]: #0 listening port port=9090 bind="0.0.0.0"
2022-05-25 08:52:54 +0200 [info]: #0 fluentd worker is now running worker=0

Here is my fluentd config:
`
@type forward
port 9090
bind 0.0.0.0

@type file path c:\FluentBit\logs\test.log flush_at_shutdown true timekey 10m flush_interval 5s flush_mode interval @type out_file output_tag false `

Here is what I get in the file written by fluentd:
2022-**05-24T17:28:16**+02:00 {"log":"{\"log\":\"**25.05.2022, 08:55:27.167** .......
The second timestamp is when the execution actually occurred. But I don't get the first timestamp.
Am I doing something funky in the buffer setup - it is not a realistic setup, just to understand how files are generated. Appreciate any comments. Thank you. -hadrian