Alright! someone with viable questions! I'm super excited to share this info with someone who wants to know.
First off, the bottom pic is not a true scrog, its more of what i call and "industrial scrog". This method takes multiple plants and fimm's them (fimming is a form of topping where you get 4 tops as opposed to one) so you have 4 top plants about 1 per 1.5 feet and each plant takes over its own little canopy space.
SCROG veg times very based on how big you want your scrog, I stop vegging when i have filled most of the screen, a few gaps and about 2-4 inches around the edge of the screen, after 24 hours of dark there will about 7 days in 12/12 that the plants "stretch" while flowering, during this first 7 day period take the tops that are 2-3 inches out of the screen and fill in the closest gaps, at this point most of your plant matter will be horizontal to the light and flower nodes will be better exposed to the light source, once this is done, clear out most of your undergrowth, large fan leaves and smaller branches that aren't getting any light can be removed so that all the energy of the plant goes into the tops that are exposed. During the next 2-3 weeks flowering shoots will rise above the screen, we want this, but if fan leaves start to develop above the screen and are covering other node sites cut them. This sounds time consuming but its really a couple min every week or so and your yield will be that much greater, the whole concept behind scrog is to have as much flower exposed to light as possible while controlling the distance of the canopy from the light for consistency. Some buds will be taller than others, if they get out of control try to train them down diagonally into a gap (if you have any) in the screen. Training buds completely horizontally will cause half the bud to not develop trichomes, and thats bad, moisture can also be an issue, make sure the under side of the canopy is well ventilated.
before we discuss your grow area i must ask, are you talking about ft or meters? I'm going to assume meters because i get the feeling I'm the only person on this site from America lol! 1.5x1.2 meters could accommodate 4 plants but it would be tight, you would only need to veg for 3-4 weeks, the top pic on this site is my current grow, its roughly 1 meter by .7 per side and as you can see, i have one plant per side, I vegged for around 6 weeks to fill this space. Really, you can veg as long or short as you want, i stop when i fill the space but i have seen people let they're tops go a foot or more through the screen before flowering, this seems like a waste to me but growing is so personal, who am I to say whats right? Thats not a hair i try to split.
Last but not least, if SCROG is too intimidating do what i did, start with LST, low stress training ties the tops down to control the canopy that way, you get a bunch of tops and a bunch of nugs! for me LST was just a gateway to scrog, i loved being able to move my plants more freely with LST but i find that i would rather have a better controlled canopy and light penetration than a big bushy plant that i can turn easily.
Thanks for the questions, keep em' coming, anything I can't answer i will research and figure out how to answer!
And now... SOME BUD PORN!
Big thanks to LBH for the gnarly bud pron!