Welcome to the Boards. My cousin went last October and made the mistake of not making advance dining reservations and could hardly get into any of the restaurants she wanted to go to.
I believe you can make them 6 months in advance. So, I would say, the sooner, the better.
Cool, thanks for the quick response. Does anyone know how far in advance park opening times are released? Just we are trying to plan are trip now and I would like to know how late the parks are open when deciding where to dine.