veg. lighting question??

If i am looking for a 3 month turn around and my strain is supposed to flower for 45-50 days should i leave my 400w MH on 24/0 or 20/4 or 18/6 for the month of it will veg?? i have heard alot of different things. I want them to be about 12-18 inches when they go to flower so as not to get to tall before harvest. i can only go 6 1/2 feet high with my 400w MH. any sugestions please... first timer

24/0, 20/4, 18/6 will all work just fine, however you want to do it. You won't notice too much difference between the 3 choices anyway.

ok cool i think ill go 18/6 for electric cost reasons....... thanks

pick the top tip off at what hieght you want