We have gone many times in Sept and the only park I do EMH for is MK to ensure we get on Dumbo, Pooh, Indy Cars etc. without too long a wait....for us, 20 minutes is too long since we're used to low Sept crowds and by using EMH, we get the most popular stuff out of the way before the rest of the "crowds" hit! Due to the Sept heat, we usually head back to hotel around noon and swim/nap and then head back out to Epcot or MGM around 4-5pm when sun is retreating!