I was just coming to ask this question. We have an 8am ADR for Crystal Palace while we are there and are wondering if we will be driving that day... I'm sure that some one on here will know the answer.
The boat starts running 1 hour before park opening.
If you need to get there earlier, the Contemporary Resort boat starts at about 6:30AM. From there you could take the monorail or just take a short walk to the MK.