you should read the link below its from the faq from overgrow.
http://www.drugs-forum.com/growfaq/766.htm
think most is covered in that link if running 1 plant per sq ft of screen almost all your training is done in the first few weeks of flowering and veg time is short about 2 weeks or long enough for the plants to just penetrate the screen if running fewer plants you would have to train some in veg and have a little more veg time if you do not time switching to flowering just right you can easily underfill or overfill the screen and it may take a few grows of growing one strain to get it just right.
instead of actuall having one large screen you can also have smaller screens that add up to the same amount of area per example attaching a 1 by 3 ft screen to a single hydro unit or soil container each holding 3 clones gives you a removable unit that can be removed from a cab to allow easier training and it also allows you to have different stages of development in each stage so you could have 1 finishing flowering and another just starting