For a 7:30 ADR, you're going to have to up and out at the MK bus stop by 6:15, as already noted. These early morning buses don't run as frequently as the regular buses do, so if you just miss one, you'll have to wait at least 20 mins for the next one. Since they are supposed to start running at 6:30, if you are out and waiting by 6:15, you should be good to go.
When you board the bus, ask the driver if it's faster to take the monorail over to the Polynesian or a boat..that you need to be there for 7:15, so need the quickest way. The driver may very well offer to drop you off on his way out of MK.
If he doesn't offer to drop you, head to the monorail. It starts running by 7am..it will take about 15 or so mins to get to the Polynesian.
If you don't want to go that route, just take a cab over. Get the cab for about 6:50.