I just checked our manuals and it is 24 hrs out (check in) from the website or kiosk. You can list 3 days out. We had 2 UAL pilots yesterday going to ORD. One was checked in and the other was not. I asked the agent if it's based on time of checked in or who showed up to the gate first. She said, it's when they checked in online first (because it creates a time stamped) so they know who's first. I see some flights tonight going to ORD and some OAL are already checked in 12 hrs out.