We went last year for 2 weeks during FD, end of Aug. to beginning of Sept., over Labor Day, and had to best trip. The crowds were extremely low, we hardly had a wait for any ride. Space and Splash Mountains we rode several times without getting off, some rides had no one waiting. We were even able to walk up to a few restaurants (Coral Reef, Garden Grill) and get in immediately at 5:00 dinner.
Many schools are already back in session way before Labor Day. Our kids go back Aug. 5.