We typically go in September. We're going this year 9/13-9/27. It's not as slow as it use to be. Disney Marketing certainly does a good job. However, it's slower than summer or other times of the year. Just don't expect that you'll be walking onto everything.

It will still be very hot. There are typically afternoon showers, so bring your poncho. That can be the best time to enjoy the parks as others clear out.