I leave my lighting on for 24/24 for the first couple weeks. Then I cut my lighting back to 18/6 once my plants get a hold and start to grow. Ive read many articles saying that 24hrs is the only way to go and how its so much better for the plants. But per the grow books I have they explain how having a 6hr dark period during the veg period is better for the plant than just running it for 24hrs aday. The books say its because the plants need the dark period to shut down and breath or release gases or something, but just as the books said and I figured, its only natural for plants to have a dark period. Thats how they've evolved in nature to grown in light then in dark, no where on earth is there a strain growing in the wild that doesnt get some dark. So like I said above, Id place your plants in 24hrs of light for the first 2-3 weeks then cut them back to the 18/6 time schedule for the rest of the veg. period or you could just leave them on 18/6 from the time they sprout until your ready to flower