These are really two separate questions; there is no minimum requirement for day campers (save for at least one day camp visit within the previous three months prior to a boarding appointment with us).
However, we recommend at least one visit per week for the sake of your dog. For many pups, this environment can be stressful until they get to know their new playmates. If you bring your dog on the same day(s) every week, they will generally have the same playmates. If you sporadically bring your dog, your pup can forget his new pals or will have an entire new group to get used to. This can be very stressful for your pooch.
On the other hand, five days a week can often be too much for many dogs, especially if they are not used to socialization and play five days a week, twelve hours a day.