Depends on room size and how booked the resort is. Places like OKW and SSR are usually at 96-99% capacity all year round. Getting a room before 4pm at OKW is like winning the lotto. Especially with 2 bedrooms and Grand villas, they are huge.
Expect it after 4pm, and usually if it's not ready till 5 or so it's because of an engineering issue of some kind.