I'm not really sure what a 24\7 impact would be on these, however what my personal aim in my tank is to try to simulate a natural environment which is ~12 hours of light a day, and then ~12 of no light so photosynthesis can cease.. a resting time as it were.
I would stick to 12 hours but if you wanted you could probably amp it up to 14.
Do you keep your lights over your sump on all of the time? I know many people (including myself) have it on a reverse cycle of our tank lights to keep photosynthesis going in a small way with macro algae growing at night in an attempt to keep the pH of our water stable but beyond that.. not sure what would happen