https://help.marriott.com/s/article/Article-34716How late can I check in to my hotel?
If you will be arriving after midnight, please contact the Hotel directly (see your Confirmation Email for the phone number) so they can make a note in your Reservation and plan for your late arrival.
Guaranteed Reservations (Rooms reserved with a credit card or confirmed with another billing method) are typically held until 6:00 a.m. the following day.
If you fail to arrive before this time, your Reservation will be cancelled and you will be charged a No-Show Fee
The amount of the No-Show Fee is based on the Hotel's Cancellation Policy and should be confirmed directly with the Hotel
意思就是午夜之后的Check in，最好是需要给前台打电话留房，否则可能会被release出来，虽然这个Help写的是通常保留到次日6点，但是有的酒店夜审的时候就release出来了。
这个和机票超售的原理可能类似，就是酒店想最大化地销售房间，过了午夜还没来的客人，酒店可能会赌一下他不来了，这样房间就可以卖给walk in的客人。
