Keep Trying. I scheduled a trip in November for a February vacation, so well beyond the 180 mark. I was able to book CRT for 6:30PM. Though granted that is a really expensive Pre-Fixe that food by itself isn't really worth it, but I understood I was paying a premium for princesses and eating in the castle.
If you're flexible about which meal you want and day you can get lucky. It just takes a lot of persistence and on rare occasions, you can actually catch a reservation day of or day before.