Last year it was mid-August.
You can still book a Room Only reservation 500 days from your check out date. For example, if you want to travel February 1 to 5, you can book a room only reservation for your entire stay 500 days from February 5. Once the 2009 rates are released you can then get the updated pricing and change to a package to add tickets and dining if you want.
The price you will be given now will be based on 2008 Rack Rates during Peak Season.