You won't get any reward points or nights credited to your account until you complete the stay regardless of whether it is advance purchase or not.
We live in the UK and always go to London for a few days before Xmas. We are going to West India Quay. We have been there before and love it. The advance purchase rate we snapped up was a lot less than half of the normal rate! If I booked it now, even at advance rate it would be 80% more. What a bargain.