I usually keep the lights on a timer about 10-12 hours. On the few occasions that I have left the lights on too long (overnight cause i passed out drunk, during finals weeks, etc.) I have noticed that the softies especially close up until the light are turned off, and then even are slow to open the next day. I suspect they get the coral's equivalent of a sunburn.
It's an interesting experiment to try 24/7 lighting. You might find that some species love the excess light. You could even try an alternating light cycle, such as 6 hours on, 1 hour off, to see what the minimum amount of darkness is needed for good growth.
Do it, try the lighting 24/7. Make I thread and I'll subscribe.