This is being done when a topic is being autoclosed (here). When a topic auto-closes, a new post is made to say that the post was automatically closed. Normally that post will be shown as unread, which can be annoying to everyone who has read all the other posts in the topic. So we mark the autoclose post as read by anyone who read all the real posts, and give it a 1 ms read time.
So if you have a lot of auto-closed topics, you’ll see those 1 ms post timing records.