iStudiez Pro allows you to enter holidays, days off and other occasions when your institution is not to be attended.  
Go to the Planner and click/tap "Holidays" button to add a holiday. 

iStudiez Pro supports schedule shift option.
There are two Schedule Shift options: Alternate Days and Whole Schedule.

Alternate Days shift option is used if your classes repeat every X days or every X working days.  
For example, if your classes repeat every 5 working days. 

Whole Schedule shift option is used if your classes are set to repeat e.g. every Tuesday and holidays are to run one or more full weeks (7 days and more).  
For example, if you study from Monday till Friday and your holidays is going to last 2 full weeks. 

Schedule shift option is set in the Settings/Preferences of the app.
Don't forget to enable the option when adding a holiday.