We were there for a 5:30 ADR last Thursday night. I was surprised how much more popular this place has become. I'd say check in early to make sure you're done in time. We checked in about 5:15 and weren't seated until 5:40. Almost as soon as we sat down the waiter was there for the drink order. Once they take that the food starts coming very quickly. If you don't participate in the activites (parade, limbo, hula lessons) then you can be out in an hour. We did all the activities and it took us about 90 minutes.
So, to answer you question, yes you can do an 8:00 at MK.