As soon as you are able.... for a couple of reasons.
If you are looking to book a sole proprietorship (as I am), availability may be limited as I can only perform at one event at a time.
My fees also increase on a regular basis. The earlier you lock in, the better price you will receive. I do not have a different price structure for 2003, 2004, 2005, etc. Regardless of the wedding date, you get the current offered price at the time of booking(every vendor may have differing policies). Although booking at the 'last minute' may get you a discount, remember that availability should be a concern if you are discerning and want a specific individual.
Good luck...
Michael http://www.musicbymichael.com 631.928.5918