I understand that as it is not within the 48-hour window.
The room has to be booked
a minimum of 48 hours in advance. if you wait until July 26, you will be unable to exercise the guarantee until July 28.
48-hour Guaranteed Availability: Limited to a Platinum member's personal guestroom. Guaranteed room availability for reservations booked 48 hours prior to arrival available at all participating Marriott hotel brands except Marriott Vacation Club International and Horizons by Marriott Vacation Club. Only during a very limited number of dates (for example, special events) are hotels unable to provide this service. This benefit cannot be used in conjunction with award usage or any type of promotional or discounted rates. At Residence Inn and TownePlace Suites, this benefit applies to studio rooms only.