For vegetative stage is better to use MH lights and for flowering are HPS will do best. As far as how long you need to keep your clones in the vegetative state it's really up to you. Technically you can flower your clones right away because genetically they are the same age as the mother plant which is usually is the plant that is ready to flower. So if you have a lot of clones(30-50) you can make SOG (screen of green): you take 3" or 4" ABS plumbing pipes, cut them in length foot or foot and a half fill them up with your grow medium and plant your clones in them. Than place all of them in one or two storage containers about 4x5x2 and flower them. You will get a lot of small plants with huge top buds. Or if you want them to grow in the vegetative state it would be up to you how long you'll keep em in that stage it depends on the size you desire. Theoretically this type of plans will stay in the vegetative state for many years as long as they receiving continius supply of light no less than 18hr a day. Good luck!:jointsmile: