You can choose to close down a slot to make yourself unavailable for that time. This will override your regular working hours. To do so, first click on the day of the lesson you want to close, then go to the desired slot and click "Edit":
Choose the far-left option—"Make Unavailable"—and click "Submit":
The slot will then appear as "Downtime" and students will no longer be able to book a lesson then:
