If it were me and it wer really important to be there by 8:30 am, I'd spring for a cab that morning. Ask the driver to take you to the Contemporary and drop you off as near to the walking path as he/she can. You'll be walking just a bit further than if you took the resort bus directly from the BWI/BWV.
Expect to pay $12 - $15 for the cab ride. Allow about 30 minutes total from the time you ask for the cab at the front entrance to arrival at GR at the MK.
Best wishes -