Until they are around 24" if possible but you don't say what strain. 2 months veg time is good. Most do much shorter but your yield better with 2 months average.
Let the plant tell you when to switch the lights. If she is already tall and lanky you will want to veg earlier.
Smaller, bushier plants may do better with another week or 2. Also, longer veg = better yield. It is the
growrs' age-old dilemma -- greed vs. impatience.
Most of these decisions are based on the growing room available.
follow my sig to see what 10 weeks veg got me.
id say if you have the room and the appropriate wattage. vegg the shit out and milk your plant for what its worht. you already have to wait 90 days for a simple harvest why not tack another 30-40 to gain a couple more ounces while youre already waiting.
My problem is gonna be room enough in the shower stall to flip 6 plants, 4 purple kush & 2 tahoe og. I have a 4x4 flo light, 20,000 lumins. The PKs are short and bushy and the T OGs are tall and lanky. They are just about 13" right now and in 1 gallon pots...anything else I should say?
lst the T OG'S to bring them down to about the size of the PK'S it will better your chance with those lights because if the T OG's get to tall the PK's will hardly get any light as fluro's dont penetrate down very far.i think its a foot