it takes about 17-19 hours. We drove the first day from 4-730 and got to Gainesville. Spent the night in Gainesville and then drove to WDW the next morning.
They slept for a while, then played their gameboys. We had bought 4 new games for the trip (for the ride home for being bored with the same old ones they had).
We gave them early b/c they were being so good. You hardly heard from them in the back. It was great