You can always book a trip 11 months in advance at your home report and 7 months at the others. So for April travel, you could call in May of the previous year for your home resort and September at the others. UY does not change this in any way.
What is important to know is which UY your trip will take place as this determines what points can be used to pay for it. Everything is based on time of the trip and not when you call.
For example, if you have an April UY and decide to travel in April 2013, that would happen in your 2013 UY. To pay for that trip, youd be able to use banked 2012 points, 2013 points, and borrow 2014 points when you called to book it, regardless of when that is.