This question was prompted by Review First post - Test reviews where often old first post reviews are possibly explained as being audit reviews. I believe audit reviews are only enabled on the larger sites as per this comment on the question What are review tests (audits) and how do they work?
On Electrical Engineering and I think I've seen the same on Pets with audits disabled several times I've seen items in the first post review queue that are days to weeks old and they already have several upvotes and edits made in the interim. While not that old here is an example from today:
While I can't tell the precise time it was asked an edit was made by JYelton at 2014-07-01 16:53:42 UTC and working back from the current time my review was around 2014-07-03 03:00 UTC so around 36 hours had elapsed. By the time I saw it the question had three upvotes and an upvoted answer. It didn't seem to require any additional action other than I did upvote it as an interesting question.
The first post queue on EE.SE is normally quickly processed so I'd find it extremely unlikely over that time a post would be ignored or skipped over continuously. I wasn't really sure if this is a bug of some sort of a feature I'm not aware of that slips a few things back onto the first post review queue?