Hi Kristi!
Thanks so much for the love! We love helping guests plan their magical vacations to Walt Disney World Resort!
The answer to your question depends on what time the Magic Kingdom opens that morning. Generally, it opens at 9:00 a.m., but will have morning
Extra Magic Hours about once a week. So, if the morning of your reservation is the morning of Extra Magic Hours, then you will be fine. The buses "officially" begin running one hour prior to the opening of the park that opens first.
I said "officially", because there usually are some buses that run for early morning breakfast reservations. These buses begin running about 90 minutes before park opening, and should only be used by people with early reservations. The problem is, they aren't guaranteed.
If I were you, and the route I normally take, is to take a taxi. You can stop at your front desk and they will be able to help you figure out the best choice. They can let you know if the park has early hours, whether a bus will be running early enough for you, and they can arrange a taxi for you if needed.
You can easily do all of this the day before your reservation.
I hope this helps! Please let me know if you have any other questions.