How early to arrive at the airport? That question has caused more than a few disagreements. Usually, though, the people arguing are travel companions. One reader recently heard a view on the subject from a gate agent.

He'd missed the boarding window for his flight to Austin, Texas. The next flight was three days away, and the airline offered only a small refund. The gate agent told him it was his fault; he should have arrived at 3:30 a.m. for a 6:30 flight.

The traveler had arrived at MSP Terminal 2 for his Sun Country flight 90 to 120 minutes before takeoff, but encountered a long, slow-moving line at the security checkpoint. He and several other Texas-bound passengers dashed to the boarding area ahead of departure time — but after the airline had closed the airplane doors.

It was maddening to arrive — panting, after sprinting from the far side of the terminal — to see the plane in place, and be denied entry. But the gate agent was following airline procedures, which are similar to those of other airlines.

Sun Country's Contract of Carriage (basically, the agreement you sign off on when booking) suggests passengers arrive at the ticket counter at MSP 90 minutes before a flight (and 120 minutes ahead at other airports). Passengers must be at the departure gate 30 minutes ahead of a domestic flight, or risk losing their reservation.

Delta suggests passengers arrive at least two hours ahead of departure on domestic flights; they require passengers to be at the gate and ready to board 15 minutes ahead of departure.

It's hard to say what was happening at Terminal 2 that early morning, but sometimes the unexpected happens. For that reason, I have changed my ways. It's been a long time since I've been among the last-minute crowd.

For the record, Terminal 1 opens at least one of its two security checkpoints at 4 a.m. daily. Terminal 2 opens one of its two by 3:30 a.m.

Contact Travel Editor Kerri Westenberg at travel@startribune.com; follow her on Twitter: @kerriwestenberg.