Hi Vikki!
You are going during what is historically a very busy time of year. However, it is also one of the most beautiful times to visit!
Dining reservations can be made up to 180 days in advance, and if you are a Walt Disney World resort guest, you can make all of your reservations for your trip at 180 days before your check in date; for example, if you're staying for 3 nights, you can make all of your reservations on the first day you are eligible as opposed to having to call back 3 days in a row!
To be honest, i've never had a problem getting the reservations I've wanted when I've made them 6 months in advance. However, I haven't tried for Cinderella's Royal Table in the Magic Kingdom in a long time. Historically, that is the hardest Table Service restaurant to get a reservation for. You have to call or use the online system first thing in the morning on the first day you are eligible to try (e.g. 180 days in advance). Online dining reservations can be made
here.
Good luck and enjoy planning your magical vacation!