Even though the flight may be delayed, that does not equate to check-in being delayed. IIRC, check-in at AMS is done by contract staff and they very well could close the desks an hour prior to the scheduled departure time (and likely move on to their next assignment). If your friend needs to check a bag or is not able to check-in (and print a boarding pass) on-line then you should make sure they are at the airport with sufficient time to make the check-in cut off. The last UA departure is the ORD at 10:55 so, conceivably, the check-in desks could close around 10am.