Hmm.. that's tough to say. Coronado is a HUGE resort with multiple bus stops. We stayed there a couple years back. Many times, we would eat breakfast and go to the lobby bus station. By the time the bus got to us, it would be full and we'd have to wait for another.
The lobby at CS is the last bus stop before heading to the park (unless that's changed in the past few years.) I wouldn't recommend catching a bus from here.
I'd say to be at the bus stop as early as 6:20 - 6:30am. The buses come around every 15 minutes. If you miss a bus around 6:30, you could catch around around 6:45. Better to be early. If you're willing to make RD at 7am, you may what's 5-10 minutes? If you get there at 6:45-6:50, no big deal.
