Since OKW has the largest number of units it does tend to be relatively easy to get in at the 7 month mark. In fact, I made a reservation for a two bedroom and a studio about three months out just this spring!
However, there are exceptions. If you are wanting a GV pretty much any time of year, if you are going the week between Christmas and New Year's Eve or the week of Easter you will probably run into problems booking. I'm not sure of other size units or times of year, but I'm sure somebody else will jump in here too.