The check-in period begins 24 hours before departure and ends 45 minutes before the planned departure time. You can either check in online and print your paper boarding passes to bring to the airport, or you can retrieve your boarding pass(es) digitally via the Allegiant mobile app (preferred). Allegiant Air provides different check-in options for its passengers, but the earliest you can check-in for a flight is 24 hours before departure. Learn more about Allegiant Air check-in policies and procedures. https://getairlineshelpdesk.com/check-in/allegiant-airlines-check-in