Your Instructors have limited accessibility ? Maybe they have a part-time job? You can mark it in ActiveNow.
Go to bookmark Instructors, later choose a concrete person. When you move down you will have limited accessibility and then you can have definite work hours for this Instructor.
Default will be made accessibility the same as opening hours.
You can change it for every day separately.
Also after opening the calendar and choosing a daily view with the Instructors division, these with limited accessibility will have washy hours – so you can see who doesn’t work those hours.