Are You asking if you have to make reservations in full week blocks? No, you do not. You can make 1 day, 5 days, 9 days .. what ever you have the points to cover.. and that is one of the beauties of DVC!
You could contact person you are renting from and seeing if they have more points to add some nights, or you could rent from someone else and hook the 2 reservations together.