"Use Year" is the month when your points will be renewed each year. It is the basis for banking deadlines, but has no effect on when reservations may be made.
The only issue would be if you had to cancel a reservation on short notice just before the end of your Use Year. If you have a June Use Year and cancel a reservation for May 15-22, you will only have until May 31 to reuse those points since they cannot be banked and will expire on that date. There is no effect of Use Year if you don't cancel. (If you cancel that same reservation at a time when you can still bank the points- there is also no problem.)
If you will normally travel at the same time each year, a Use Year that starts that same month would be best (but ...again... only if you have to cancel on short notice).
Enjoy!
