The majority of airlines, including American Airlines and United Airlines, allow passengers to check-in online from 24 hours up to 45 minutes before a domestic flight's scheduled departure time. The latest online check-in time generally increases to 90 minutes for international flights. Online check-in saves passengers time at the airport.
As check-in times can vary between airlines and routes, a passenger should visit the airline's website to check its rules. To check-in online, a passenger needs to find his reservation on the airline's website by entering his six-character confirmation code, or record locator, and surname. The ebookers.com FAQ section offers advice on checking in online together with links to the websites of different airlines.