It's generally recommended that guests wanting to attend morning extended hours at the parks be at the bus stop around 90 minutes before extended hours starts that day because buses start running +/- 60 minutes or a little bit before that. If MK opens at 8:30 for extended hours that day, the first bus from a Disney resort is likely to pick up between 7 and 7:30, which means cutting it close (too close for my comfort) if you have to ride to MK and then walk to CR. It's looking more and more like you might have to book a private car transfer, to be sure of getting there on time with 2 kids in car seats. I'd book a private transfer and then try to push my ADR later!