Sorry to revisit an old topic, but I was trying to come up with some answers to this question. Over the past couple years, I've only done a few grows, and I've always counted "vegetative" growth from the moment I see the first set of leaves on the little seedling (not the cotyledons). From there I grow them for about four weeks.
My plants obviously don't get as big as they could, but once I get up and going again, I am going to maybe experiment with a six week veg time.