The 2010 points reallocation suggest that there are, in fact, too many available weekend (Friday/Saturday night) rooms.
If you are wanting availablility, then booking your reservation to start Fri or Sat at the exact 11+7 date may, in fact, better ensure you get the following week.
Booking at anything less than the 11+7 opening would not help in this case (because other 11+7 guests got their complete week before you tried to reserve
Now, there are probably also certain periods where this thinking does not work i.e if you wanted a post-Thanksgiving trip, then starting on Sunday would probably have better availability than starting Saturday, because Thanksgiving week trips may exend through Satuday..