Clones should not be under 12/12 unless you want them stressed because they dont know if its time to flower or grow roots, giving them atleast 16-18 is more like it.... Hes right about 24 not being needed, but try to stay on the veg side of things until you are sure you like your plant size. And you can take clones for a while into flowering, but that also = more stress.... The earlier the better, try to take the cuts earlier...
On the flower side of things, the 24 of dark really does help ramp up production, but is not needed ... Bud growth takes place at night, thus a longer night means more bud.... Try 14 to 16hrs in the dark youre plants will love it, and you will see production in a matter of days
Stressed plants =lower production= less happy smoker......