I've had approvals take as little as a day but my last two new apps (a watch face and a data field) which I submitted last Friday, September 16th took the full three business days. I think sometimes other stuff takes priority, which is why they say it can take up to three days. I believe that if it's been more than that you are supposed to email them.
I've seen approval in as short a time as the same business day, normally within 2 business days, but maybe going as long as 4 business days.
I submitted something new this past Monday, and it was approved on Wednesday...
Now here is something that is super secret so don't tell anyone or post it! :) (not really secret, just something to note...)
When something new does get approved, it's display on the "new and updated" line on the main screen of the app store is based on when you submitted it, not on when it's approved, so if you submitted it yesterday, it won't show on the main screen of a few other things have been updated in the mean time..
Hint: as soon as you get the "approved" email, do a quick update if you want your app to show on the main app store.
