Use year has nothing to do with when you can make reservations. It's just when your points renew each year. All points use is based on date of stay and the points are actually in your account 3 years in advance, so you don't have to wait for the use year to start to make a reservation.
For example:
You have an April use year (April 1 to March 31)
You want to make a reservation for September 2009. This would be in your April 2009 use year. You could use banked 2008, current 2009, borrowed 2010 points for this reservation. You can call in October to make this reservation at your home resort (11 months before date of stay). Say you want to stay in June 2009. You could call now for your home resort because it is less than 11 months away. Non-home resorts would be 7 months, you could reserve an arrival up to April 16 today (reserve up to 7 nights).