The Marriott Mobile App has been downloaded 2.3 million times and app users can use the app to check-in at Marriott Hotels with their Apple or Android device after 4pm the day before their reservation and up to two hours before arrival. Mobile check-in is available at all 329 Marriott properties in the U.S. and Canada. After checking-in with the app, guests can pick up their room key at the Mobile Check-In desk.