Boarding begins anywhere between 11:15 (new reports based on the new arrival times) and 11:45 (when they historically began boarding). So if your friends would like to be on board the ship early, than an early port arrival time is better. (When they arrive at the terminal, they are given a boarding number based on their Port Arrival Time. The earlier the PAT, the lower the number.) If they aren't planning to arrive until the crowds clear out, then they can select a later arrival time. Usually by 12:30/1:00, they have called open boarding and boarding numbers are irrelevant.