Yes to answer your question you can keep the plants in vegetative stage as long as you want but from my experience the plants double or sometimes triple in size during flowering stage so i usually keep my in vegetative stage for about 2 months n there are usually around a foot foot and a half tall but i am also using an mh bulb for veg and a hps for flower..i to used cfls once n i didnt get a good yield or fast growth but ya never know stay positive.