Originally Posted by
Bierjunge
But thank you guys for answering my initial question whether or not it is possible to leave the airport between two flights on the same itinerary.
After clearing customs in ATL, you will need to follow the signs to exit to Atlanta, instead of following the signs for connecting flights. You'll exit into the International Terminal, which isn't connected directly to the MARTA station. You will need to take a shuttle bus to the Domestic Terminal and catch MARTA there. Alternately, you could take a cab straight to the hotel.
But the next day, you can take MARTA directly to the Domestic Terminal, where you'll check in for your flight to FL (and check your bags too if needed).