I would use the bus so you don't have to park at TTC and then Ferry or Monorail to MK.
The bus from Sports is almost always direct to MK for Park Openings,but can share with Music and Movies at other times.
6:30 AM is the most often "quoted" start time for the buses.
During my stay in May at All-Star Sports,I was up early 2 Mornings and decided to see just exactly how close to 6:30 AM the FIRST bus to EACH Park arrived.
Remember,this is just a "snapshot" of two particular Mornings.
Day 1
6:18 AM----Magic Kingdom
6:56 AM----Magic Kingdom
6:58 AM----Magic Kingdom
7:00 AM----Magic Kingdom
7:01 AM----Hollywood Studios
7:12 AM----Magic Kingdom
7:12 AM----Epcot
7:16 AM----Animal Kingdom
7:16 AM----Hollywood Studios
7:17 AM----That's one hour of my life I won't get back!lol
Day 2
6:17 AM----Magic Kingdom
6:30 AM----Magic Kingdom
6:38 AM----Magic Kingdom
6:54 AM----Magic Kingdom
6:55 AM----Hollywood Studios
7:11 AM----Magic Kingdom
7:11 AM----Hollywood Studios
7:11 AM----Epcot
7:15 AM----Animal Kingdom
7:16 AM----Time To PLAY!