If you are going to change the light cycle 24 hours of darkness is the way to do it. However, I have done the same thing myself and half the plants hermaphed. I really wouldnt recommend changing the light cycle. Especially not while your in flower. What I would do if i were you is keep the plants separate and just take both of your 150 watt lights and put them both over one set of plants and then keep your 400 watt light on the other set. Like i said you could try to change the light cycle but yes you are going to risk hermaphing.