That Lowryder was (sortof) on 18/6, but the box was NOT light proof, so it effectively had 18 hours light, 6 hours of twilight. I have done similar on all my plants pretty much, for stealth reasons (if the box is off all of the 'working' day, its a lot stealthier if your landlord fancies a surprise visit, and cooler at the hottest bit of the day too..). I havent checked what effect any different light cycles than this one have had though.