The monorail starts running at 7am. The buses start rolling about 6:15-6:30. Those early buses are provided for those guests who need to get to parks very early, for tours or ADRs. But, they do not run as frequently as regular buses do. Be sure to leave at least an hour from the time you leave your room until the time you need to be at the podiums to check in. A bit more time is nice.
Going from resort to resort early in the morning is a bit tougher. If you have to get to CM's at 7, you need to be at the MK bus stop, at your resort, by 6:15. You really do want to be out there that early. As you board the bus...ask the driver if it's faster to walk or monorail to the CR from MK. He may very nicely offer to drop you off at the CR rather than have you walk. And walking is quicker!!! It takes about 8 mins to walk via the sidewalk, from MK. The monorail won't be running early enough for you to hop on and get to CMs in time to checkin at the podium.