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this comment was made almost 1h after the one at the root of the thread

you can make changes to your posts up to 10 minutes after they were originally created — see: https://news.ycombinator.com/newsfaq.html#:~:text=minutes%20...

[minimaxir]

That is not what that feature does, it just is the time your comment is publically shown.

Users have 2 hours to edit comments, and the button was gone within 1 hour.