United Airlines check-in policy allows passengers to complete their check-in process up to 24 hours prior to their flight departure time. To do so, passengers should have their passport and/or ticket number handy when accessing the United Airlines website or mobile app. Customers may also print boarding passes at any self-service kiosk located in United Airlines airports up to 60 minutes before the scheduled flight time. Those who choose not to check in online can visit an airport counter during regular business hours before your flight departure time, or alternatively at least 45 minutes prior if checking baggage with an agent at the counter.