Many differnet people use different light times...24/0, 18/6, 16/8, and 14/10, but the last one not very many people use.
The thing to remember is how long do you want your plant to veg for? Longer light cycles takes the plant longer to sex, whereas shorter mean sexing quicker, but it also depends on the plant itself...it will sex when it's ready. I personally use 16/8, 2 reasons: 1) less energy used 2)they show sex earlier.
Plants will still grow during your dark period...it will help strenghten the plant since it will do any minor repairs to itself, and build stronger roots. People will argue that no dark is fine and that the plant will do repairs on it's own...this is true...but it takes more of the plants energy to do it.
As long as you tend to them and baby them, it won't matter what cycle you use...you should get some healthy beautiful girls

