It depends on when the park opens. The the park boats/buses haven't started yet, the easiest way is to take the small boat (blue) over to the CR and walk to the MK. The blue launch circles WL/CR/FW and runs from 6:45 - 10pm or later (I've heard 11 or 11:30, so I'm not sure of the exact stopping time.)
We used this route when we had a early CRT b/fast while staying at MK. The boat ride is 5 minutes or less and the walk, 10, maybe 15. If you don't want to walk, you could take the monorail from CR too. It goes CR/Poly/GF/MK.
When you get to the MK, they'll have a separate entance open for ADR's, usually to the far left.