Vail Marriott does something weird like this for reservations made for the January-April 2008 time frame. If you book a stay (not using Platinum override - meaning Plats not signed in) starting on a Sunday or Monday then the reservation has to be for 7 nights or more otherwise it results in a ** NO ROOMS AVAILABLE FOR REQUESTED DATES ** message. Stays commencing on any other day of the week can be as short as 1 night.