uwnyuD can you retrieve the post via the REST API and check if the UTC date in the JSON payload is correct? GET /api/post/<id>
Flarum works completely in UTC internally and only when the date is shown to a user in the browser it is converted by the browser into the current locale.
If the value is wrong in the REST API it's possible that Flarum is reading the date from MySQL thinking it's UTC when it's not. I think MySQL is the only part of the process that doesn't store timezone together with the time, so for all DATETIME columns there might be issues if PHP and MySQL aren't using the same timezone.
I don't think Flarum has an explicit setting for the PHP timezone. The task is probably left to the PHP PDO driver to convert DateTime instances into valid MySQL dates, but I'm not sure how PDO choses the timezone by default.
