As has already been posted, it's 7/11 months prior to check in. However, there will be times when there is no corresponding date. For example, let's say you want to book your home resort for a stay beginning on Jan 30, 2011. Eleven months prior would be Feb 30, 2010 but that date doesn't exist. According to Caskbill, you should be able to book that stay on Feb 28, 2010 but the reservation software MS uses may not let you do so and they may tell you to call back on Mar 1st.