Yes it all right. During veg. growth it really doesn't matter about light. You can change it all around all you want. Your best bet is to be consistent. In veg. A plant would grow in 6 on/18 off, but it would be much slower. I would suggest the 18/6. It gives it alot of light(which is needed for the plant to make energy, More light more energy more growth) but still gives them a break(as well as gives your light a break). I've read that when outdoor, a plant will actually grow more at night and "collect" light energy in the day time.