Our family loves the Hilton Head Resort. I have wait listed the resort 3 times. We were granted the wait list at Hilton Head 2 of the 3 times it was requested. Just know the resort only has 21 studios ( we always wait listed the 1 bedroom).
As a rule of thumb, waitlist as soon as you can to increase your chances. Shorter waitlists ware easier to get than a longer one.
We got a short weekend once at the Grand Californian. I kept adding one extra day one wait list at a time. We ended up going from 2 night to a 6 night vacation.
Best of Luck getting your waitlist!