Originally Posted by CO 1E

To clarify this a bit: any upgrades that are processed after the online checkin window has opened are still prioritized in the order of elite status and fare class within elite status. Time of checkin only breaks a time between two elites on the same fare class. For example, if there is one seat left and two Platinums with H fares are contending for the seat, the Platinum who checked in earlier will get the seat.