Can I add business hours for a specific day/holiday of the year?

Yes! In the "Business Hours" section of the Settings tab, click on "Add a day with irregular hours."

Select the calendar day you wish to edit by clicking on the calendar icon. Then, select your business hours. You may also choose "By Appointment" or "Closed."

Note: if you choose the "By Appointment" option, mark the first box "By Appointment" and the second box "Closed."

When you are done adding irregular days, click "Save Changes."