This may have been caught and fixed already…
When a topic is set to close after 24 or 96 hours after last reply it appears close immediately.
24 are the only values I have tried.
The following post is added after a minute or so:
This topic was automatically closed 0 minutes after the last reply. New replies are no longer allowed.
This has not been tested on latest - but it was in this version:
Discourse 1.3.0.beta7 - https://github.com/discourse/discourse version 875a013ec76e7ce0cbb95a61223cbbd16ed31d4a
I did however check the first line of all commit comments for the last 17 days - only one mentioned “auto” and it wasn’t to do with closing a topic.
The last post was 10 days ago however.
But I was expecting the topic to close 24 / 96 hours from the time it was set to auto close (if there wasn’t a new post before then).