Airport upgrade processing goes by status, then by checkin time.
Here's how it would look:
Name Status Ckin time (time elapssed since checkin)
---------------------
Bob US1 12:05
Jim US1 08:00
Joe US2 23:59
Sam US2 20:00
Mike US2 19:00
Dick US3 23:59
So you see, it definitely helps to use online checkin to check in at the 23:59 mark to get to the top of the list in your status.
-JC