It's something to do with the "second chance" mechanism. Here's the email I gotten from dang explaining the issue:

>It's an artifact of the re-upping system. '1 day ago' was the original submission time and '1 hour ago' was the re-up time. Lots of explanation here: https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que.... Sorry for the confusion!

>See also https://qht.co/item?id=11662380 and links back from there.