Use Year is the month every year when your points are renewed. Use Year has nothing to do when you may make a reservation. you can always make a reservaton at your Home Resort 11 moths in advance as long as you will have sufficient points available at the time of the reservation. You may always make reservations at non-home resorts 7 months before arrival.
Use Year does determine your banking deadlines and thus might be important if you need to cancel a reservation. In general it might be best to have a Use Year which begins just prior to when you would travel so, in the case of a cancellation, you would still have opportunity to reuse or bank the points returned to your account.
For trips in August, an August or June Use Year would work best for you and you would not want a September or October Use Year since it would limit your travel options in case of a cancellation.
With an August Use Year, cancelling an August reservation in June would still give you until the end of July (of the following year) to use the points. If you had a September Use Year and cancelled an AUgust reservation in June, the points would need to be used by August 31 and could not be banked any longer.
There are no January, May, July or November Use Years.