I always count my days like this: from sprout to first set of true leaves (single blade usually) is a seedling. veg is from then until the time that they start to flower. You can veg for as long as you want, as long as it's not an auto, and you keep your lights at 18/6-24 hrs. Thats why you see alot of people with big vegging plants...the bigger the roots and the more budsites, the bigger the harvest. It all depends on the space you have to work with.
Also if you compare soil grows to hydro you will see a significant difference in growth at the same age. Every growers skill level is different, and every strain grows different.