Hi Tony West Oz, you should have plenty of time to explore Oahu. The bus service there is actually pretty good and dependable, however, you could grab a cab, too. You could go visit the Arizona memorial, the Punch Bowl (cemetery), Diamond Head, Hanauma Bay, the Toilet Bowl (if it's still open), and the north shore. Then come back through the pineapple fields. In fact, there may be kiosks in the airport to book a tour that would include those spots. We booked ours through the hotel we stayed in. If you don't want to do all that traveling after flying for so long, maybe just take a cab and go down to the beach at Diamond Head. You could go to the Royal Hawaiian and have brunch out on the lanai. There are also a plethera of lounges, restaurants, shops, etc., at that area. If you can, please go see the Arizona, it is really spectacular.
One thing I would suggest, is to check into the ship. You could go over to Diamond Head, then return to the ship. Get your sail and sign cards, then go and explore some more.