Google says 9.5 hours, but I figure more like 11-12 due to traffic in Atlanta.
if you go thru atlanta in the middle of the night wednesday night like i did in 05, you will zip right through ;D
You must plan your trips through Atlanta very carefully. Trying to make it through Atlanta on weekdays between 6-10 AM or afternoons between 3-8 PM is never a good idea. Outside of those times you should be ok but best times are definitely between 8 PM and 6 AM.