I think I may go earlier if I were you. We had a flight that arrived at 10:00am and were at the port by 11:00. By then a line had just started forming to get onto the boat (which didn't start til 12:00). We were the 10th family in line. The hour or so waiting flew from just looking around the port, getting coffee, talking to other cruisers etc.
I know you don't have to check in since you are doing the land and sea, but if the limo picks you up at 11:30, you'll get to the pier around 12:30 and there will probably be a long line.
Just my thoughts.
Have a great trip!