For most airlines, online check-in begins 24 hours prior to departure on domestic and international flights. It is advisable to check in as soon as possible to verify flight information and resolve problems that may arise.
Online check-in allows passengers to select a plane seat and print a boarding pass. More seating options are available the earlier this process is completed.
For domestic flights, online check-in is available up to 45 minutes before takeoff. For international flights, online check-in is available up to 90 minutes before takeoff. Consult with individual airlines for specific check-in policies and possible changes in flight schedules.