Assuming you are talking about 2010.
You probably have a while, since most schools will probably be back in session on January 4. However, if that first week includes the Marathon, the smaller resorts will fill very quickly as soon as the 7 month window opens.
My advice is to book it when your window opens (unless you need to borrow points) - it's a long time to next January and you can easily cancel without penalty if/when your plans change.