If you want to go on Saturday morning, jump on it now. Those flights book up fast, especially now that they (USAir) have eliminated the 8:00 flight.
One thing concerns me about Airtran - if they are not filling seats on a selected route, they may just stop service. For example, they stopped service from Pittsburgh to Philadelphia on a short notice. USAir dominates PIT and the low cost carriers don't survive (Spirit, National, Vanguard all pulled out on short notice).