It may be that a lot of people are booking the Fantasmic dinner package at Mama Mia's and want to be done in time for the show. A 5pm PS isn't bad, though. Eat a late breakfast (10:30) or early lunch (11:00) and you should be ready for dinner by 5.
I love just walking around at MGM or sitting on benches and watching others walk (okay, after our first 3-4 rides on the ToT!!!) This park has so much to observe. The more I visit, the better appreciation I have for the Disney mind -- all the little details. Guide books & experts say you can easily do MGM & AK in one day or less each. Yes, you can whirl through, go on the rides, see some shows, and be on your way. But to really get the most out of a park, you have to 'stop & smell the grease paint' so to speak.
Hmmm, wait, this is the restaurant posting area, sorry, got into my 'enjoy the theme parks' mood again.
Which ever you choose, you will certainly appreciate the atmosphere - and isn't that what WDW is all about?