How long until my school is actually running?

One afternoon is enough for a single-branch school. The smoothest order: branches → programs and classes → schedule patterns → students and their families → place students into classes with their payment model → invite teachers → switch on message channels.

The step that matters most is placing students into classes, because that is where the payment model is chosen. A placement without a model is refused — exactly so that no student can attend without a pack to deduct the session from.