Some believe that you can do it toolate.. I am notone of those. You can tie it down (LST) or super crop them, I'd do it.
As far as how much a plant grows, that depends on the strain as much as any thing else. Some plants grow very little (slowly) in veg and other gow faster, and the same holds true vice versa.
One thing that I've noticed it that most plants "stretch" during the first three weeks of bloom and establish their internode lengths at that time.
Do a search for supercopping... here, and also at you tube.