At the moment, Zenefits automatically adds US Federal holidays to the holiday calendar for each Time Off policy when the policy is created. Administrators can manually remove these holidays and add new ones, e.g., for specific countries. However, anyone who is assigned to a particular policy will have its holiday calendar, regardless of their actual work or home location. You may follow the steps here to edit the holiday calendar.
Holiday calendars do not roll over, so they must be completed every year.