1. In my experience, early embarkation is not possible on the PG. They may make a few exceptions, but they don't really want you there early (this could have changed in the last year or two, of course.)

2. I am guessing you're not doing Regent Air. I'm sure you know that if you were, you'd be given a dayroom, and be allowed to disembark late. As for bopping around Papeete, it's possible that perhaps the ship would keep your luggage for you for a while, but probably not that long. For a 10 p.m. flight you'll want to be at the airport by 8 or before. If you want to get out of Papeete, you could just dump your luggage at the airport and rent a car for the afternoon.