Use Year has nothing to do with when you can make a reservation.
If you will need to cancel reservations on short notice, Use Year will have an impact on your ability to reuse or bank the points freed up by the cancellation. (If you have an April Use Year and cancel a reservation for March in late February, you would not be able to bank those points and would still need to use them by March 31 or they would expire.)
Otherwise, Use Year is simply the month when your points are renewed each year. There are no January, May, July or November Use Years.
If you will usually travel in the fall - a September/October Use Year would likely serve you well.
Enjoy!
Edited to correct missing Use Years.