I think it really depends on the flexibility of your kid. We went last year and it was great! The lines were short and it wasn't too crowded. She lasted until right after the second parade. She slept through haunted mansion, the walk back to the car and the transfer back to our room. The timing was actually perfect for us too. We got to the park a little after four so she was able to have her afternoon nap before we went. We are going back this year and taking our 9mo.
Eta: she had just turned two when we went.