the way i figure is as follows:
-when it pops the soil i call it a seedling for about a week.
-then its starts veg. for about 6 to 7 weeks for me but however long a veg. you want.
-then start 12/12 for flower and if its an 8 week strain, i usually flower for 9 weeks. sometimes longer if i dont have plants ready to go in the flower room.