Not yet, but it's on our list! and an HN user who works for them has personally committed to budging me if I don't get it done in the next month or two.

The way it works right now is that we have a keyboard shortcut to open the archive.org page for a url posted to HN—kind of like the 'past' and 'web' links we display at the top of /item pages, except faster [1]—and we use that when trying to find the date of an article. Sometimes the archive doesn't have it yet, in which case we click the link to add it.

1. Actually a number of HN features have started as moderator keyboard shortcuts. It would be fun to release that software, but... time.