Are you using a controller? Is your array dimmable? If it is, peak daylight hours are preferable between 6-8 hours I think. If you're dimming the unit, it wont matter how many hours outside that as your corals won't be exposed to peak intensity.
For example, some people have their LEDs programmed to simulate sunrise/sunset of particular GPS co-ordinates. Because they're running their lights at a fraction of the daylight intensity, you can keep them on longer without stressing your corals.
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