20 hours per week feels fine to me, at least there is some slack for unplanned experiments. I certainly do have rooms in my house which I actively use for less

20 hours per week feels fine to me, at least there is some slack for unplanned experiments. I certainly do have rooms in my house which I actively use for less than 20 hours per week, and I don't consider them useless. A single class per week is ridiculous, though.