well the 24/0 is for max growth. then slowly timing the light back helps keep it from getting droopy, i usually do about 4 days each step from 24/0 -> 12/12. so the total shift from 24/0-> 12/12 takes about 2 weeks. keep in mind its NOT flowering til its at 12/12. so the day you decide to start this, add 2 weeks to start 'flowering" and another 2 weeks to start seeing some buds.
and yea 12/12 under the veg light for a day or 2, and i put in some redder CFLs, then the day i switch to the high pressure sodium, i change the CFLs to daylight ones, so its a nice transition, a few weeks later, they are all red lights.
keep in mind, when you switch from veg to flowering, measure it, if its 1 foot tall there, you can end up with a 2-4 foot tall plant. if its 3 feet tall when ya switch, expect 5-9feet. the reason for this is the plant is like "wtf where did the light go? maybe ill grow taller in case something is blocking it, i gotta find that light again!" and it shoots up, and fills in (gets bushier). this kinda sucks cuz your internodal spacing (spaces between branches) gets huge, and that space is mainly wasted. the slowly backing down of the lights keeps this from getting outa hand.
my first grow, they were about 18 inches at 5 weeks or so when i changed them to flowering, and 12/12, and they ended up a few weeks later about 7feet, i had to tie them down eventually. (or cut a hole in the cieling of the closet they were in, and my gf said no....)
they grow a lot dude. i wouldnt go more than 30inches MAX when indoors, that ceiling will be lower and lower by the day lol.
Ill toss ya a freind inv, shoot me some questions man, i do this about all day, every day lol