Keep your 5:00 reservation. You'll never see the parade, exit the park, wait for a tram and drive to the AKL in time for a 4:30 ADR.
You should, however, have no problem getting to the Contemporary for 6:45...provided you are seated at Boma on time. My advice would be to get to Boma as quickly as possible after the parade and check in early. That should give you a better chance of getting seated on time. They don't seat all of the tables at 4:30 so there will be some open at 5:00 and you shouldn't have too long a wait.
Dinner can take as much or as little time as you want. Boma's buffet is set up as pods so you won't have to wait in a long buffet line. Simply go to the pod with the items you are interested in. Oh, and don't miss the Zebra Domes for dessert!
Enjoy!