If your home resort is SSR or OKW, there is probably no need to "start calling" (assuming you mean for day by day reservations). I've never called day by day for OKW and have always been able to get what I wanted during the 11 month window. Call Friday, July 6th for those reservations.
If you want to book BWV standard view, of feel a need to book day by day, the first day you could call would be July 2nd, to book the night of June 1st.