3-4 weeks, but you will need good knowledge and equipment.
Photoperiod plants are superior in every way to autos in my opinion, you won't regret your decision.
In vegetative growth, it's not a problem at all. You can continue as usual. ^^
It becomes much more of a problem if it happens during flowering, or if the light stays off too long.
@Golden, the Afghan was severely stunted so not going to put any effort into them. Just going to kill them and move on to the Bubba Kush seeds that I put down upon discovery of those aphids. Cheers
@Herbie101, never got high from any of the prior grows. too much light? dunno, dont care just want to get stoned for over a years work n waiting. thanks man