as others have said, you may find inventory becoming available closer to the date, but it can come open at other times too.
Don't just check the full time you want, if you're looking for a week. You may be able to piece together a couple of shorter reservations to get the interval you want.
Sometimes shorter intervals start to appear inside of 90 days because the booking restrictions are lifted. (They may appear earlier but can't be booked; but inside 90 days they can be booked, and some people may "chop" their reservations to the length of stay they wanted if it didn't fit into the booking requirement).