Many school curricula use a model of five or six “classes” taught throughout the day, broken up into even chunks, and combined with lunch and breaks. This makes planning the movement of large numbers of children possible.
But if you didn’t have a school structure - if you were instead dedicated to each student’s learning - how many subjects would you teach?
The answer is probably, “It depends on the day, student, and subject. Maybe one. Or one hundred. Or zero.”
Having said that, a default broad schedule makes sense for some who crave a bit of order. Probably the most basic is the best: have one morning subject and one afternoon subject.