RCI cancellation policy is pretty straight forward.
1. You can cancel a reservation if it is less than 24 hrs. (Watch the Saturday evening website shut down, customer service is not open during that time either).
2. After 24 hours, you can cancel and get your TPUs or points back of you purchased the "points/TPU protection". You do not get the $299 exchange fee even with their insurance. For the price they charge, it will depend on how many points or TPUs you are using for the reservation to make it sensible to buy their insurance. You might find better value buying an insurance that covers your whole trip for less.