We had an 8:05 PS at Crystal Palace last May and we were out of there by about 8:50. I think we saw all the characters and we even lined up for Piglet. But as the others have said, you've got to get there early, and not just to the MK; you've got to get to the crystal palace before everybody else if you want to be seated before them. So here's the deal - you can either enjoy the empty park before your breakfast, but then you might not get seated for a while and probably won't finish before 9:00 OR you can rush right to the Crystal Palace and probably be seated early and finish early and enjoy the park for a little whiule before 9:00. But remember that "rope drop" procedures constantly change and sometimes they just open the park early anyway, so you may get out at 8:45 and find yourself in a crowd.
One tip, if you're really concerned about time, and getting out of the CP on time, bring in varying denominations so you can pay for your meal and scram. Nothing worse than having a deadline to meet and having to wait for the waitress to bring you your check, then wait for here to come back for your credit card, then wait for her to reurn with the slip for your signature.