Hahah.
We've run into similar challenges with our business. We want all our team members to have flexible schedules, but we also need to hear from them within a given day. We've settled on "be available daily for 7 hours, they just don't have to be all in the row." If someone's not going to put in a full day or be around, we appreciate knowing ahead of time. That seems to work fairly well.
Nice - we should start practicing that. It's just some freelancers freelance pretty hard.. and I don't think 7 hour daily would work on some.. although admittedly my setup isn't the type that is as busy as Foxycart!