Most public holidays are set up for you already, but as holidays can vary for a number of reasons, It is possible to add additional public holidays through account settings.
Add public holidays to your account
Click on Account, then sub menu Settings in the side bar menu.
Navigate to the tab that reads Public holidays
Click Edit to open the additional holiday field, now click the area 'Pick one or more dates' to begin selecting additional public holidays.
Use the calendar to navigate to relevant dates and select them by clicking the date in the calendar.
To remove additional holidays, simply click on any selected date, or to remove all additional holidays click the x at the right hand side of the field.
Don't forget to click Save when you're done.