I'll use wattage as a 'marker' as it is easier for most to understand wattages than other measurements.
There is no limit to the hours you can put light above the tank. 24 hours is not a problem for the plants, however there isn't much point because once they've had enough they will 'shut' their leaves and take no more. You then risk supplying light for algae to grow if there is the slightest defficiency. Also as said above let the plants and fish have their rest.
12hours light/12 hours dark is what they will most likely get in nature. We tend to go for shorter periods as all we want to do is give the plants enough light for their growth and minimise the algae's chances, therefore the norm in planted is 8-10hours. Often we will just use 5-6 hours when we first plant and gradually increase it each week.
If you have 2 lights in a hood and to your eyes it looks bright on the substrate then when you raise the light it may look darker. Not necessarily less light reaching the substrate though. More likely that it is now covering the whole substrate better rather than being intense in one area and not too good in others.
You prefering the 10K over the 6700K is more than likely you prefer the colouration. It may seem darker or brighter but it will be as 'bright' to the plants if they are the same W.
By the way lights are not costly. You already have the equipment. the tubes are only costly if you pay for the following 8 letters to be printed on them: A Q U A R I U M. I think they use a very rare and expensive ink to print this word

Get a decent normal tube that fits your unit (wattage and length) from a normal hardware store. It is the same bulb without that expensive printing on it.
As an example in the UK a standard 18W T8 'non aquarium' tube will cost under £3. A decent 18W T8 'non aquarium' tube will be circa £5. The Arcadia standard AQUARIUM version £11, Arcadia Plant verison £15 and ADA NA £20.
The standard under £3 will have a poorer CRI (maybe 765/865) meaning it is not as good quality (not as accurate in colour rendition etc) therefore we would buy the 'circa' £5 one which would be a 965. Same wattage, same output. Marketing sells the aquarium ones and some of the aquarium ones may not be much better than the 765/865 cheapy household one!!! They rarely tell you the actual CRI on the aquarium ones. Just loads of pictures of spectral graphs.
My flourescents weren't raised above the hood!! They were 4-6" above the water. My LEDs are raised even though they are lower wattage because they are much much brighter W for W. However being brighter doesn't mean the plants are getting more light. It means your human eye is seeing more light, but I can see from plant growth that the plants are also getting more light!!!
I wouldn't suggest that lowering lights will raise the energy that much. It will for the plants directly under it but others further from this point may get less!!! Depends whether how many tubes you are using and how they are spaced/positioned.
As for colour temperature. If I lower my LED light close to the surface I can see rippling on the wood cabinet directly in front of the glass. Guess what. The light seperates out and I can see red/blue/green in this rippling. These are 5500K LEDs and from the rippling I can see the 'full spectrum'.
I have grown plants under pure 7500K, 6500K, 4000K, 4500K, 3000K and have never noticed any difference in growth speed. I have noticed differences in colour but turn the lights off and the colours are all the same. It is the bulb colour that gives red a deeper red or a nearer peach etc.
Summary:Run the light for 12 hours, 14 hours, 16 hours. If you have the desired result then you have your answer. There is never any harm in trying things like this because if it doesn't work you just go back to what did work (reset and try something else.)
This is a tank with a white background.
This pic shows 0.9WPG of 4500K. The tank has a pink hue:
This pic shows 0.9WPG of 6500K. The tank has a green hue:
This pic has 1.8WPG. the 2 above combined. The tank is white:
These are T5HO tubes though. Do the colours look the same to you? Does the white look white? The above is my eyes perception of the colour. Your eyes may seem different. Look at Monet's paintings as he got older. The colours turned more and more yellow because that what his eyes saw as he aged!! Not all of us will see the same just because we are not old. Each person's eyesight and perception can differ dramtically.
What do you see in the above 3 pictures?
AC