If you check in right at midnight on the date online check in opens, you shouldn't have any issue being onboard before Noon. This obviously would be less of an issue if anyone on the reservation is Platinum or Diamond as you can do online check in two days earlier and should be able to grab the earliest time slot.
The biggest constraint might be can you actually get to the port early enough? Even if you have an 11 AM Check in time, I wouldn't recommend the Noon appointment.