Your Business Plus card guarantees room availability provided you make your booking at least three days before your arrival (before 12 noon local time at the hotel). (businesstravel.accorhotels.com)
Checkout can be as late as 4 p.m., and you receive guaranteed room availability 72 hours prior to your date of arrival. (rewardexpert.com)
You will also get guaranteed room availability if you book at least 72 hours before your stay. (upgradedpoints.com)