code: public void removeHoursFromDay(ProjectCalendarHours hours)
     {
        if (hours.getParentCalendar() != this)
        {
           throw new IllegalArgumentException();
        }
        m_hours[hours.getDay().getValue() - 1] = null;
     }
docs: Removes a set of calendar hours from the day to which they
  are currently attached.
  
  @param hours calendar hours instance