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The minimum required check-in time with checked baggage is 40 minutes before the scheduled departure time for US domestic flights from SEA (30 minutes without checked baggage), so arriving at the airport one hour before is more than enough, unless perhaps if you're bringing some TSA-unfriendly items or have reduced mobility.

The minimum required check-in time with checked baggage with Delta is 40 minutes before the scheduled departure time for US domestic flights from SEA (30 minutes without checked baggage), so arriving at the airport one hour before is more than enough, unless perhaps if you're bringing some TSA-unfriendly items or have reduced mobility.

https://www.delta.com/us/en/check-in-security/check-in-time-requirements/domestic-check-in:

When you’re traveling within the United States, we make the suggestion to arrive at the airport at least 2 hours prior to departure. For most airports, you must be checked in at least 30 minutes before your scheduled departure time (airports requiring additional time are listed here, [copied below])  Additionally, you’re required to be at the gate and ready to board 15 minutes before scheduled departure.

Exceptions Minimum Check-In Times by Airport, where the check-in time deadline is >30min:

The minimum required check-in time with or without checked baggage is 30 minutes before the scheduled departure time for US domestic flights, so arriving at the airport one hour before is more than enough, unless perhaps if you're bringing some TSA-unfriendly items.

The minimum required check-in time with checked baggage is 40 minutes before the scheduled departure time for US domestic flights from SEA (30 minutes without checked baggage), so arriving at the airport one hour before is more than enough, unless perhaps if you're bringing some TSA-unfriendly items or have reduced mobility.