If a doctor is not around on a certain date, how do I block it from making an appointment?

To block from adding an appointment, add Blackout Time. Add it in a similar way as Doctor on Leave. 

1. Go to Calendar.
2. Click on the space of the Doctor Leave row.
3. Select Black Out Time and fill in the rest.
4. Click Save. 
5. Any attempt to add an appointment during the Blackout Period will cause the warning in the red box to appear.