Im not able to comment on this question, as i dont have the experience of trying different light cycles.
But i happened to come across a thread yesterday that you may want to look at?
The part i thought was very interesting, was the information supplied by Chronic Chrissy, 5 posts down the thread.

http://boards.cannabis.com/indoor-li...-question.html

Its only food for thought, and it was enough to tempt me away from 24/0 but everybody has their own thoughts
GunBarrel Reviewed by GunBarrel on . 24/0 vs. 18/6 Seedlings/clones/veg. period - Does 24/0 have any negative effect on the plants? What does everybody recommend? Rating: 5