Since you're a 1K, don't forget this just in case you're on a full fare ticket:

1K Guaranteed Reservations
You are guaranteed a reservation, even on sold-out flights, on all United, TedSM and United Express® flights anywhere. You and one traveling companion must call 1K Reservations no later than 6 hours before your flight and no earlier than thirty* days in advance, and purchase an E-TicketSM in United Economy® Y booking class fares**.