Provisional Reservation Timeout(AKA auto-cancellation of provisional reservations)
This is the time in minutes that an online reservation can exist in the provisional state. A provisional reservation has not yet been paid for and reserves the assets in the fleet. Once a reservation is paid for, it becomes confirmed. (of course in the back-office you can make a reservation confirmed even without payment if you need)
If a reservation has not been paid for the specified time period, then the reservation is cancelled in the system. Cancelled reservations can still be viewed but the assets in the fleet are now available for other bookings. i.e. the inventory is released back into the available pool.
Go to "system" - >"settings" -> "online" tab -> then near the bottom of the screen you will see provisional reservation timeout.
Read here for more information on Provisional Bookings