Add 4-5 weeks veg time if growing from seed, or more, dependent on strain & grow space. That's just letting them grow naturally w/ 2-2.5 sq ft per plant. Stretchy strains will be up in the lights if you veg too long, unless you have lots of overhead. Non-stretchy varieties will give better yield if you let 'em get bigger before going to 12/12.
That's just one middle of the road way to approach it. Some people prune & shape plants early on, veg a little longer to get a fuller canopy in a scrog or similar. Some grow 12/12 from seed in a more tightly packed sea of green.
