You'll make it. We had 8 am ressies in AK, and we made it.
Buses start running 2 hours before park opening. You'll want to be down waiting for a bus by 7:30 am (I recommend the main bus stop). Once you get to MK, take the monorail over to the Contemporary. The worst part is waking up and getting the kids out the door by 7:15!
Also, let the lobby conceirge know about your ADR. They'll be able to advise exactly how early to be out and waiting for a bus!
Have fun!
PS. If you don't want to be up and out so early, consider taking a taxi. It will only cost $15ish, and the trip is maybe 10 minutes.
PPS. If you drive, parking will be complimentary. At the gate, show your resort ID and tell them your there for the breakfast.
