From the GF, you will take the monorail or boat to MK, the monorail (or possibly a bus) to Epcot, buses to DHS and AK. Buses start running by 6:30 each morning. The monorail starts by 7. Boats I'm not as sure about.....at least an hour prior to park opening.
If I were at the GF and needed to get to CM's for 7:30, I would be out at the monorail platform just before 7...maybe 10 mins prior. That should get you to the CR in plenty of time.