Originally Posted by
MSPeconomist
Personally, I would aim to take an earlier skytrain. Arriving to the terminal an hour and a half before departure seems risky to me, especially if you're not very familiar with ATL airport. Security lines can be long, depending somewhat on the day of the week and time of year.
There aren't really lines at 4 am, and AA uses T for flights to MIA. Maybe I'd leave at 3:45? But not a lot before that. Also, since they don't have precheck, the entrance for security is "right behind" the AA counter.