We went in november of 2004 and I got the 2005 guide in September or October. It's a must have for us at Disney so you should be able to get it before you go.
Mo
I just got the 2005 guide a little over a week ago...while I don't have it with me right now, I do recall that they mention when they release the new edition somewhere in the first couple chapters. I think they shoot for September-October for the following year's edition.