Operational hours refers to the hours that the system assumes are business hours for your organization. By default, operational hours are assumed to be 12:00 AM to 11:59 PM, Monday through Friday. This can be configured for a ticketing application in the Admin tool by locating Applications > [Ticketing Application] > Operational Hours.
You can add organization-wide days off in Admin by locating Organization Settings > Days Off to declare days during this time that your organization will not be operational, such as holidays or inservice days. These days off will be taken into account when the system calculates resource availability, SLA and task deadlines, and task durations.