The Alamo car rental company's operating hours are from Monday to Friday 6:00 AM to 11:59 PM, and Saturday & Sunday from 7:00 AM to 11:59 PM. However, Alamo's customer service line is open 24 hours a day, 7 days a week. This means that you can always book, pick up, or drop off Alamo cars at the airport, no matter the time.