getting tall small tent

Agree with the commenter below, try reducing the distance to the light. I also had one case when I had to additionally stop the growth of the plant by placing a ring on the main stem of the plant (the plant was 160-170 in 40x40x120), as if this stops the growth of green mass at the moment when the plant needs to change to flowering and stop growth. I'm not entirely sure about this, but I've read articles that said that if you stop the movement of nutrients along the bark of the main trunk, the plant will redistribute the energy flow to the fruits. What do you think of this trick?

very much depends on intensity of light, but 21" is fine. assuming light is properly powered for teh area of coverage, distance from canopy should be more about how even the coverage is, without sacrificing too much in middle or end in a net loss of energy applied (weighted average of multiple locations throughout canopy should be proper). if you start to see light burns or plant is wilting/cowering from light, then you can break a branc - only slightly.. hst? supercrop? some stupid label is applied to it, lol. just bend it till the branch goes horizontal, support it so it can heal. it'll form a strong knuckle at bend within 1-3 days. if there's still likely vege growth left before it stops, you need to make sure it's bent at a low enough spot you don't have to do it a second time... not a huge deal but more stress than necessary isn't optimal. a weaker plant might hermie at some point.

Aside from the month it takes to reach sexual maturity from seed, there is no absolute minimum or maximum period required for veg. It's your choice. Cutting them back will cause them to bush out, or horizontally train them into the net. Then flip when your happy with the situation. Not really enough information available from the photo to comment on other factors. Might help to see a front view, top to bottom. They look healthy, great job!

They are stretching because the light is too far away. About 16-18 inches in veg and 12 inches when flowering is ok. Otherwise bend/tie down the taller plant so it is closer to the height of the shorter one........this is what the net is for. 18/6 is optimum too, by the way. In future, you are probably best to only grow one plant in a tent that size.