MRBS modifyer

i want to modify the MRBS system so it would fit my needs. I want to use the MRBS system to book a ice field with three locker rooms. I would have 4 rooms, ice field and the 3 locker rooms. When booking the ice field and locker room I'd like the the locker room to be booked starting 30 minutes earlier and 30 minutes longer. The offset would be entered in the form when booking the room.