I've seen HN do this once before. It took a post from a day ago and changed all the timestamps to be "current time minus a few minutes". It was this thread [1], specifically the first two comments in this subthread [2] had their timestamps faked. The third comment is from after it had been resurrected with the fake timestamps.
[1]: https://news.ycombinator.com/item?id=30510400
[2]: https://news.ycombinator.com/item?id=30511216