The few times we've had early breakfast or tour ressies, we've always taken the bus. At least at POP there has always been one bus that starts running I believe at 6:30 for character breakfasts and such. You may have better luck asking this on the Transportation board.
Just want to add, when you get to WDW the only CM's that really know what's going on with transportation are the CM's in the purple pants. They are the bus drivers and they have the answers.