Total travel time from MGM to AKL is about 20 minutes by bus (a cab can probably do it a little faster). The problem is of course wait time particularly after Fantasmic when everyone is leaving, which can 1/2 hour or more. Note many others have same idea (particularly people staying off-site who want a cab) so you should not assume that you can get a cab any faster than a bus at that time. I would just stick with catching the bus.