How to specify min and max lesson teacher shall have on one day?

You can do this in teacher's constraints:

Notes:
- you can specify to not to check these values on the Saturdays/Sundays. So the teacher shall have 2 lessons each day on the Monday-Friday, but they can have 0 or 1 on Saturday.

- please make sure that you do not require unrealistic demands here. It is strongly recommended to add this and similar requirements later. If it is not possible generate a timetable, it will be even more impossible to generate it with requirement that each teacher shall have 2-5 lessons each day. See: A good way to generate your timetable