The concept of a 'No Service Day' is related to 1CoreSolution's prorated billing system. With this system, you can define the working days of your center on your calendar and allow customers to make no payments for the days marked as 'No Service Days'.
Access Path : Center Dashboard > Setup > Prorated Tuition Billing
Federal holidays will automatically be added to the 'No Service Days Listing' as no service days. You have the option to remove them from the list by clicking the close icon next to each holiday.
To update the default list of no service days for your center's holiday or local holidays, you can simply select the date on the calendar.