Self debarkation people leave first. You have to be able to carry all of your luggage unassisted by staff or porters. RCI deems this to mean carry-on sized pieces only. No luggage is allowed to be transferred to the pier like it is for the other passengers who are leaving by the color-coded groups. When they can start leaving depends on when the ship is cleared by Customs, and of course that depends on when the ship arrives.
Booking an early flight is a gamble. People will report that they got off the Allure (or Oasis) in plenty of time to catch a 9am flight from FLL, but that is no guarantee that it is happens every time.