Buses start leaving the resorts headed for the parks by 6:30, but run less frequently that early - about every half hour or so.
You want to be ready and waiting at the bus stop BY 7 AM. When you get off the bus, walk past the MK entrance and up the monorail ramp, board the monorail, and ride to the Polynesian. Enter, turn left, go past the Kona coffee counter and the Kona Cafe, and check in at 'Ohana (and, respectfully, the restaurant's name IS 'Ohana - it means family in Hawaiian, so the placement of the apostrophe is important; thanks!)