You'll clear customs in ATL. There was a thread about this a few days ago.. will try to find it.
Ahh nevermind I see you were
the original poster for that thread.
You'll clear customs in Atlanta just like any other US customs clearing. You'll need to re-clear security after clearing customs. The minimum connection time is 85 minutes I believe. Very early in the morning the place is dead - you'll be in and out quickly.