I think it's important to know what bulbs/ballast/Kelvin you are using as well to have any sort of idea on PAR.
I voted 4 hours or less. MHs run 4 hours on my tank. Mostly because the lights are too strong for my LPS in the shallow depth of this tank, so I can't run them for the 6 hours I would like to. When I transfer this fixture and all my livestock to my 90 I will run it for the full 6 hours, and I will be upgrading the reflectors and bulbs.
I run actinics for 10 hours a day. One KZ Fiji Purple, and one AquaScience 17,500K.
1. Tank Depth?
14-15" from water surface to sand surface.
2. Light type/wattage/height from water?
2x250w DE Coralife 10,000K on electronic ballasts (bulbs came with fixture, will be changing out), 8 1/2" from water surface.
3. Reflectors?
Crappy ones. Same shape as the typical DE in fixture reflectors, but just smooth mirror finish. Will be replacing them.
4. What coral do you grow?
LPS.
5. Do you run carbon or anything else to 'clear' the water?
Carbon - 1 week on, 1 week off.