Symmetry Holiday settings

After opening symmetry, go to the operations tab and select "holidays"

Here you will see a table showing the calendar for the entire year, you can scroll up and down to move forward to future years. 

To assign holiday dates, click on whatever date you need to designate as a holiday, and click assign, then this screen will appear

Select the holiday that will be on that date, and hit OK, this will adjust the door codes to not open for those dates.