daytrip to NYC is possible (hundreds do it every day), or DC, or anywhere in FL for the most part. What kind of food/experience do you want?
If you do NYC, for example, you could depart ATL at 8am-ish, get to LGA at 10:30 or so. Cab it into town, walk around a liitle, have a long leisurely lunch anywhere, depart 6pm, arrive ATL at 8:30. (there are earlier departures and later returns during the week; these times were for a random Saturday on August.)
Have fun!