I don't veg for a particular time. I go by heighth. Each strain has it's own heighth potential so you will have to experiment some. I like to turn my over to flowering generally speaking at about 12". They still grow 2 1/2 to 3 1/2 ft depending on a few factors. Shorter plants use light more efficiently. Having your light too far away is a common mistake. It causes plants to 'reach' for the light, making them leggy. Get them as close as your ventilation and light size will allow. Obviously, bigger lights put out more heat and need to be farther away. You could alway try light movers or air cooled hoods. I keep my 400w MH at about 10-12" away.

To also answer gaz2020, flowers start appearing about 1-2 weeks after switching to 12/12 schedule. Male flowers usually start appearing first, so if you started from seed, Save the women and make babies, Kill the guys.