Just need to be there early enough to make bag dropoff and be in preclearance hall before 1030pm. Normally security/US CBP is a breeze at that hour. However I would personally not get there less then an hour before flight. Sometimes they close the security lanes over by US departures and force you to use the main security. You then have to make your way through the connection halls to get to US CBP. This isn't normal, but has happened a number of times recently due to construction.

Lounge will be closed by time you arrive at airport. However, if you arrive really early, you can use the normal security lanes, enter the domestic/international portion of airport and use lounge their. However need to leave time to then follow connections over to and clear US CBP.

ETA - Went by above poster's posted time for closing. It's actually listed as 2030 (which is 830pm, not 1030pm) they close. Thus flight will be handled as a normal international flight. Clearing will be done at ATL. Access to lounges will be normall international lounges. Thus if paid J or STE+ can use Skyteam lounge.