We usually stand around for about 20 minutes or so, waiting for more people to arrive, then stand around another 15 to 20 deciding where to eat. Then we either all eat in a group or if we can't agree on a place, we split into two and eat. Then we stand around deciding what ride to ride then go ride, etc.
However, the group's always splitting into sub-groups and coming back together again. Also, you can stay as long as you want - 5 minutes in the hub to say Hi, after lunch, midnight... People are always floating in and out, it's no big deal, no huge commitment!