I think there is another show after the 5:15 one...so you should have time to make it to the MK. I don't think taking the resort monorail will delay you. It only stops at the GF after the Polynesian, then you're at the MK. Also, it would take 5-10 minutes to walk from the Luau (closer to the GF) than to the TTc which is all the way on the other side of the Polynesian. You're better off taking the boat or the resort monorail. JMHO.