They tend to open the "ears" at around 11:45. By 11:30 the line to board can be kind of long.....if you get in line at 11:30, you'll probably board by 12:00 however. If you get in line at 12:00, you'll board by 12:10. The terminal opens at 10:00, and there is probably ten or twenty minutes worth of pre-boarding check in that needs to be done. So if you arrive at 10:00, you'll hang at the terminal for an hour and a half or so before boarding.
We got to the terminal around 11:15. We were checked in by 11:30. Rather than get into a long line, the kids watched cartoons, met Snow White and Mickey Mouse, and we got in line around 11:55, boarded by 12:10.
You won't be able to get into your stateroom until 1:30 - pack your daybag light. Lunch is served the moment you board and the pools are open.