Using Disney transport, catch the bus from BWV to the MK, then monorail or boat to the GF from there. Resort-to-park buses start running at 6:30 a.m. for early ADRs and you probably should be at the stop around that time because the buses won't be running as frequently until one hour before the park opens.
If you're willing to take a cab it would be much quicker. If you're getting into a cab at 7:30 a.m. you should have no trouble making an 8:00 a.m. ADR at 1900 PF.