Your light setup will have a lot to do with it yes, but also take into consideration the genetics of each seed, especially if its bagseed. One strain may explode and grow really fast maturing well before the others, where as the other seed(s) with possibly different genetics may take a few extra weeks in veg to mature. One sign you may look out for though, is during your veg cycle the branches of the plant will grow symetrically to one another, side by side from the main stem, where as when the plant is reaching maturity the branches will begin to grow asymetrically and grow uneven off the main stem.