When we went in June the Wonder was NOT the only ship in port, the Norwegian Sun was as well (and I think is in port the same day as the Wonder every other week.
Our shuttle driver said the port is CRAZY before 12, we arrived right at 12, and although busy it was manageable and we had no waiting, check in, customs, and by then we walked right on the ship. You can go early but will spend more time waiting. My thought was relax in the hotel and then spend less time waiting.