Found this on the Mom's Panel:
Getting information on bus schedules for early character breakfasts is confusing. If you ask a Cast Member "What time do the buses start running to the parks?" they will always tell you, correctly, that the [regular] buses start one hour before scheduled park opening. HOWEVER, if you ask them "What time do buses start running for character breakfasts, then the answer will be different, since there are special bus schedules and routes set up to ensure that guests can get to their early character breakfast meals. In the case of early character breakfasts at the Magic Kingdom (Crystal Palace and Cinderella's Royal Table, or "CRT" as you call it), the character breakfast buses start running at 6:30 am.
For other readers, who may have similar questions for other parks, my understanding is that the character breakfast buses for the other three parks start around 7:00-7:15 am. You can (and should) confirm this character breakfast bus timing at your resort when you check in.
Regarding the time the park opens, it may vary slightly depending upon the crowd levels. My experience for a 8:05 CRT reservation was that we were let in immediately when we got to the parks at approximately 7:45 am. To make sure that I give you accurate information I confirmed with several Cast Members and the general concensus is that you will usually be let in around 7:45 am, but it could be 7:30 am if it is busy, and it will always be open no later than 8:00 am for an early character breakfast.
Good Luck