In the past, the GI Bill would only provide a certain amount towards flight training; however, now you can complete all the training as long as the flight school has a degree program. I'm currently at UND Aerospace using my GI BILL. The GI BILL pays for exactly what the flight school says it would cost an "average" student. So in other words, if you happen to finish early there is no advantage and if you need more time, then it would be out of your pocket.

Best of luck,
Anthony.