Here are some facts I was able to pull up.
A plant that shows sex at the forth week of vegetative growth can be kept in vegetative growth for a few more weeks to allow the plant to generate more node regions (leading to more branch and leaf growth). When the plant is flowered, this extra stage of growth should help the plant to achieve optimal results however the grow time is extended by a few more weeks to obtain this.
Bud production does not increase at the same rate as plant growth. Bud production depends on your growing environment, your strain's genetic makeup and the amount of nodes the plant has. All nodes are potential bud areas, but every strain has a genetic threshold for bud production.
It is possible to get more bud with lots of plants that are flowered as soon as they're mature (which also keeps them shorter and smaller), than extending vegetative growth with less plants until they reach their maximum height and size. The time frame for the shorter option also produces more bud turnover per year.
Here's the important part of the subject of 12/12 before flowering
Problems with 12/12
If you switch to 12/12 before pre-flowers have shown, you may encounter the following problems:
1. Stress-related sex problems (hermaphrodites)
2. Abnormal bud growth
Early-induced flowering* isn't the same thing as forcing your plants to flower. If you force flower a strain before it has pre-flowered it will flower at roughly the same time as a plant from the same strain that has been flowered after calyx development has occurred naturally. Force flowering simply acts by stressing the plant into a crisis condition.
You will get the best out of your plant by waiting until it starts pre-flowering before switching to 12/12.
http://www.marijuanahydro.com/flowering.html Here's the site.