And, in case it wasn't explicit enough from heynowirv, it is *not* the entire month but the DAY. You can reserve up to 7 nights starting on a specific day. So if you want your vacation to start on September 22, 2015, you would try to make the reservation starting on October 22, 2014. If you were to call on September 22, 2014, you'd be able to make a reservation for August 22, 2015.
Hope that helps!