Advisor - These teachers have to teach in too many classes at the same time

Typical example of this situation – Let’s say, that we have small school with 9 subjects, 3 classes and 8 teachers.

Then we want to create some free lessons for teachers. It is fine, until we set, that 6 teachers have “time-off” on exact same period (on picture below it is third period on Wednesday).

It means, that for these three classes, there are only two teachers available for teaching on this period. This situation software evaluates as clearly mistake in inputs.

As solution, we have to check time-offs of all other teachers, then mentioned by advisor on highlighted position, and allow some periods.
Of course, in real timetable, this is more difficult, as in this example. It need not be only time-offs, but you have to check also other constrains you had created (i.e. maximum periods per day for teachers, constrains forbidding teachers to teach on specific periods, and others).