How high should I veg?

I have 2 gals in a 2x2 currently week 8. They are 18 in away from my mars hydro ts2000. My light can't go any higher in my tent so should i start flowering when there 12 in away? Don't mind the nute burn on the one in the back it's my first time but I got it figured out lol

Im a new grower and there may be strains that Im not familiar with but unless thats one of the strains that flowers grow back down toward the ground, you might have a problem.

Take the plants current height then double it to get a good idea how tall they will be when done stretching...

You need to grow a strain a couple of times to find out it traits, most ime will nearly double in height, personally I wouldn't grow straight up I'd have them tied over and trained.
These are nearly 4 weeks old.

I flipped them a couple of days ago, I'm anticipating double the growth but I'll keep that growth horizontal so the full plant gets intense light rather than only the tops.

SD

Update: Thanks for all replys, installed trellis in hopes of helping them grow out. To much stress on top of plant? Also how tight should trellis be?

you want to tie it up fairly well, your wanting it to hold the colas up and in place, but you can allways tighten it up ater on