Reservations can be booked 11 months in advance (in your case, April 2013), so I'd say no earlier than March 2013. And that's only to give yourself time to find someone with the home resort and amount of points you would need for the reservation. But if you haven't rented before, hang around the board, learn about the different options, and educate yourself so you're ready when the time comes. Good luck and congrats on the baby to be!