I read something recently (might have been linked from here, can't recall) about what happens if you add a person, arrive early, arrive late etc at a restaurant, and how the flow on can be a major drama for everyone. Cafes need to have rules, unfortunately, but maybe wait staff could say "we can take your order now, but the kitchen staff won't be ready to start it until 12:00, is that ok?". Probably would have ordered another round of drinks in the wait. That said, a local group that appears to be made on the "Single Parents Alone Together" premise from "About a boy" meets in a park nearby. I reckon if they worked it out so that a coffee cart rocked up at their meeting time, everyone would be a winner!