The MaxHoles constraint limits the number of free time (holes) for an instructor on a day.
It has one parameter: a maximal amount of free time in minutes (between the first and the last class on a day) that an instructor is allowed to have without a penalization.
For example, reference _MaxHoles:120_ translates to a maximum number of two hours of total free time between the first and the last class on a day.
If required, having more free time is prohibited. If preferred or strongly preferred, the excessive free time is penalized.