They've been posted.
It must be fascinating to be a volunteer who stays at the starting line all day. I always head out with the hardcore 100-mile crowd at about 7 AM, but as the day goes on, the riders get more casual. You start to see fewer jerseys and more feather boas, ribbons signed by family members of cancer survivors, Girl Scout troops riding in uniform, and that sort of thing. The event actually caters to a broad spectrum of riders. I do feel kind of bad for the people who are going up Canada Road at 11 AM or so; they'll be riding in the heat all day and there's no shade on that hill unless you go under an overpass.
As with most pursuits, I end up hanging out with those more hardcore than myself. That sort of riding is more focused, solitary, introverted.