Every day, Walt Disney World extends the hours of one park either one hour earlier or three hours later than regular operating hours for guests staying at Disney resorts, such as Disney’s Grand Floridian Hotel and Spa or Disney’s Art of Animation Resort. Disney calls this guest perk Extra Magic Hours (EMH), with the opening of the park one hour early being morning EMH and the closing of the park two hours later evening EMH. The park with EMH becomes THE park of the day to visit for many Disney guests (and even some staying at hotels outside of Disney World). The lines for rides, characters and food are greatly inflated at the EMH park compared to the other three. You should never visit a park with Extra Magic Hours…except when you should.
If you have a park ticket with the Park Hopper option (allowing you to visit more than one park in a day) and you can arrive at the park thirty minutes before morning EMH begins (i.e. arriving at Magic Kingdom at 7:30 am, having already eaten breakfast and ready to go for an 8:00 am opening) and you promise to leave for a much less crowded park once the hordes descend and the lines become too much to handle, you should definitely take advantage of morning EMH when it fits in with your touring plans. Using the FastPass system, you can easily ride most of the rides in Fantasyland and Tomorrowland before 11 am on a morning EMH day at Magic Kingdom. Most people will not arrive at the park until 10 or 11 am, preferring to sleep in and have a long breakfast. You, on the other hand, will have seen all of Future World at Epcot and be ready for the World Showcase by the time they arrive.
Evening EMH are a different story. People will have no problem arriving late and staying late at a park with evening EMH. The park will get crowded in the afternoon and stay crowded throughout the evening. Your Disney vacation will be much more magical if you hit the hay early and visit the parks right when they open, well rested and ahead of the cranky, tired crowds.