Ситгуру эти 4 часа упоминает не только для curbside но и для киосков, хотя сама Дельта говорит, что в киосках можно это делать за 24 часа.
https://www.delta.com/content/www/en_US ... tions.html• Our airport kiosks can help you do everything you'd normally do at the counter — faster and easier.hecking in via the Kiosk
You can check in using the kiosk,
any time within 24 hours of your flight.
• Find your itinerary by inserting your SkyMiles card, passport or any credit card (with the same name as the traveler), scanning the barcode on your printed Delta itinerary or select TYPE on the kiosk screen and enter your confirmation, ticket or SkyMiles number.
• If more than one passenger is traveling in the same reservation; select the passengers who are checking in.
• From the Trip Summary you can make a change to an earlier flight, upgrade your seats or cabin, check bags, add Trip Extras or simply Continue to complete check in.
• Take your printed boarding passes and any receipts you need for your records.
• That's it —
you've completed your airport check-in. Now bring your checked bags to the nearest baggage drop (marked by a red Baggage Drop sign) and proceed to security.
Did you know if your next or return trip is within 24 hours, you will be offered the option to check in for the flight from the kiosk!
А как оно там есть на самом деле - узнаете на месте.