I have been in september. the crowd is smaller than the summer, considerably. However, you may be surprised at the crowd that will be there. Disney World has become such a popular destination that off season small crowds are no longer so small.However, In my experience the smallest crowds and the most beautiful time to go is in December between thanksgiving and Christmas. As far as the shorter times the park is open, You would be amazed at how much more you can do and see in the off season. Eventhough the parks are open from 8 a.m. to 7 p.m. in the offseason, You will get more done than you can in the summer because the crowds are smaller. The average line wait in the off season, in my experience, is 30 minutes, and that is being overly generous. The times my wife and i have gone in the ofseason, we have, many times, been able to walk right onto most attractions. The only attractions, i find, that stay crowded year-round are splash mountain, big thunder mountain, space mountain, You know, all the major thrill attractions. However, even their lines are considerably shorter. Go in the offseason, definitely, After Thanksgiving and before Christmas, if possible.