I booked a guaranteed interior (IF) on a cruise at the end of this month, and my cabin was assigned about 30 days pre-cruise. I was upgraded to a mid aft location (IB).
It seems like this is around the point that all balcony cabins and better sold out. Until this point, it looked like there was still quite a few to choose from, but once all the cabins were assigned, the entire balcony class showed as sold out.