We usually try to arrive at the port between 10:30 and 11. Check-in doesn't take very long and then we get in the boarding line. In 4 previous cruises, we've always begun boarding by 12:15. While my DW waits in line, I take my DD and DS and walk around the terminal and view the model of the ship. Usually around 11:30-11:45, some Disney characters will make an appearance and we'll get a picture made.
The time goes by pretty fast and the boarding line gets HUGE!! My advice is to get in line early.
Have a great cruise!