I this question, I replied to a comment. The comment I replied to then appeared below my comment with a timestamp in the future:
The comments will now just appear out of sequence, but at the time the timestamp was in the future.
This has been posted a couple of times in the past, but it appears to be happening again.
Update: There have been reported incidents of this also occurring in other areas where timestamps are generated, such as the closed question notices and in chat.