When we re-up a post, which I did with https://news.ycombinator.com/item?id=40560010, you see a relativized timestamp on the front page and on the /item page (i.e. the thread). See https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que... for explanations of why.

The original timestamp is displayed on all other pages, so you can see e.g. from https://news.ycombinator.com/from?site=samcurry.net that albinowax_ submitted the article first; and of course the item IDs are sequential so that's another way to compare the two.