Hours / days / weeks is the correct answer :D.
Seriously now, if the change is small and you don't change description and your extension doesn't use dangerous permissions, it can be only about one hour.
Otherwise it's about one day, maybe whole weekend if you submit it on Friday (maybe).
But sometimes somehow, I think the extension is flagged for manual review and it takes whole week or two.
I have to say, it's better now, and most of my updates are now handled within one week.