Delays on flights in and out of Atlanta are usually due to afternoon & evening thunderstorms.

I would have no problem with a one hour connection in Atl (heck, I sometimes leave my house about an hour and 5 mins before my scheduled departure time).

In the 100's of Airtran flights I have taken out of Atlanta that leave in the am, I can only ever remember one that was delayed and that was only by about 15 mins. I don't think you have anything to worry about at that time of morning.