What you have is a Port Arrival Time. When you arrive at the port you will check in and receive a boarding number.
At Port Canaveral the earliest PAT is 10:30-10:45. They usually start boarding the ship 11:15-11:30 and have everyone waiting onboard by 12:30-12:45. At this point they go to open boarding meaning you check in and walk on.
So if you show up a little early at 12:30 you should be able to board before 1:00