go with 24 hours on unless hps or mh is your lamp, plants grow twice as quick, and roots grow extremely fast here some 11 day old seeds under 200 watt cfl 24 hours on
I like to use a more natural approach to growing...the plants respond better that way.
Just read my first post and that will help you make a decision...all techniques are good, as long as the end product is what you want!