It depends on how well you can store it and where you live. Keep it dry, and of the ground. (like in a garage or shed, on a pallet or something similar)
If you live in an area that has below average humidity (West/Southwest US or up North) then you might be able to get away with about 8-9 months worth of seasoning, otherwise - in the Midwest, I recommend 12 months.
I am currently using apple wood that was cut in July 2008, and it burns very nicely. However, when I started using wood from this batch about 6 months ago, I still had a few pieces that were too high in moisture content.
Give it at least 8 months in ideal storage conditions - and then put a medium size piece in your firebox or in a lit
charcoal chimney and see how it reacts. If you see that moisture is boiling out of the ends of the stick, then it's still too wet to give really good flavor. Also, how long does it produce REALLY white, billowing smoke before it settles down to the thin blue? Of course, most wood will produce white smoke at first - but after about 45 seconds of burn, that should go away, if you're dealing with well-seasoned wood. If it doesn't go away that quick with your test piece - give it another few months and try again!