For a Delta Airlines flight, you can check in online or via the Fly Delta app starting 24 hours before your scheduled departure — this lets you get your boarding pass early. In person at the airport, check-in desks and kiosks generally open around 4 hours before departure. You must complete check-in before the airline’s cutoff (around **30 min before domestic and 60 min before international flights), and arrive early for baggage drop and security.