High-availability maintenance windows are often planned for a time where activity is at its lowest so as to cause minimal disruption to customers, though which also require unusual work schedules for the employees.
An Internet service provider, for example, may schedule a maintenance window for Sunday during the night hours.
Schools and businesses often automate the management computer systems; the information technology staff can use software to automatically install software updates during non-peak usage hours when the school or business is closed or at low activity.
Instead, a full virus scan is scheduled during the maintenance window, but is unneeded at each startup.
For small businesses with only a few employees, it may be simpler to just go around and manually apply updates at each computer, rather than spending hours trying to set up deployment through a maintenance window.