At my airfield before the days of full 7-day ops (but not 24 hours cos the local council won't allow it) we used to staff weekends with 2 controllers each 9 hour day, taking a 1 hour lunch break in the middle. On saturdays we opened at 8 am and closed at 5 pm, while sundays we opened at 11 am and closed at 8pm. Some operators obviously had difficulty handling that because on one occasion, there were three aircraft holding one sunday morning when we arrived to open up!