We always travel in September and my experience has been that crowds levels on weekdays are rather low--our biggest problem has been that they will close down all slides/attractions if there is a lightening storm within a certain mile radius and not reopen the attractions until it passes--of course the benefit of this is oftentimes masses of people will leave the park so then when the slides reopen the park is often virtually empty
In terms of wait times I do not recall having ever waited more than 10-15 minutes for anything