I would book in as soon as you can. I dont know about your area, but where we are, the waiting lists are all longer than 12 months. Most are around 18 mths where we are in sydney.

I think its a good idea to call the centre you like and if their list is long, book in before your baby is born, and if you decide you dont need it anymore you can call the centre and tell them.. but if you dont book in early it might take a really long time before a spot becomes available.