PhilStone,
Full credit to M1TEL for this solution to your night service scheduling issue.
You simply set the system to go into Night when you want. Do not use the schedule for returning to day service. The users are responsible for returning the system to day service when they open for business.
This takes care of weekend and holidays as the system will remain in night service.
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Occam's Razor - All things being equal, the simplest solution is the right one.