Not sure?

You can veg as long as you'd like, but expect your plant to double or triple in size during flower.

 

Not sure why you switched to 18/6....24 keeps them growing faster....you would benefit from elec savings at the 18 hrs though.....top them IMMEDIATELY....otherwise, they will stretch WAY out and be lanky....they are long sticks at this point...flowering them would give you long sticks with a bud on top.....They appear very sparce....what size light is over them and how far away from the plants is it......they look like either its a weak light, or its too far away, or both....I would choose a height so they all can be topped at the same size....this will add a bunch more tops that would be about the same height (nice even canopy).....You have a lot of space that can be filled with tops....lt could easily quadruple your yield as opposed to flowering whats there now.....YT
Edit....pic an imaginary plane where everyone will be the same size an top them..
Let some branches come up an THEN flower them....wont take long since they are established already....YT

 

Use all the tops you cut as clones

 

Thats a great idea since he doesn't have any mother plants.....Then he has a clone or 2 off everyone....not sure if they are all the same strain, but if not, he will have clones off his favorite....THEN he can turn his favs it into a mother plants.....Personally, I just take cuttings when I'm going into flower.....When they outgrow my starter cups (8oz styro coffee cups), I put them into solo cups...they can go thru a cpl toppings in those...before they are too big, I'm ready to use them....I do hydro too, which allows a LOT of plant in a smaller container.....I use 6 plants in my area and they each need about 8-10 tops for max yields....I dont have space in my nursery for mothers....I always run 3 strains so I would need 3 mothers..... If he intends on doing plantlet crops, he WILL need a mother plant, or his cuttings will have gotten too big....EVEN THEN, I got a buddy who does plantlets, takes cuttings going into flower, then just cuts them back to 1 top when he is ready for them....by then, they have insane root systems and a thick stalk...his plantlets ultimately get fatter tops....lots of great options when growing.....Grafting becoming popular....you can graft 3-4 (and even more) strains onto the same plant...long as you keep track of which sections are which....nice to have a mother with 3 or 4 stains on it...No such thing as CROSS CONTAMINATION from the host plant either....It works, I had a grafted plant a few yrs ago with the original host strain and 2 others...YT

 

I grow strange. When flowering is almost done i sprout the next round and 12/12 from seed until sex shows, then i harvest and Reveg all the girls, add them to my canopy and repeat.

 

I like 18-6 cause they do need a littoe down time think of outdoors no plant gets 24 hr light . U can do 24 but i prefer 18 plus u save $ on the hydro bill.

 

I started mine on 20-4 for a week now 18-6 for 3 weeks

 

They DO NOT need down time (whatever technical term that is)....photosynthesis occurs when there is light and does not without it.....whoever told you that is pulling your leg....That one if the great things about indoor controlled enviroments, you can IMPROVE on what nature created.....you cant have 24 hours of light outsite in the continental U.S, but that, by no means, says they dont continue to grow if provided with it....equatorial varieties get maybe 14 hours of daylight during summer equinox....and most states will NEVER GET even 18 hours of light during the summer.....If that 'theory' were remotely true, why would ANYONE run lights 18 hours....That MORE than anyone gets outside....AHHH, because they continue to grow when receiving light.....I've been growing for 39 yrs now and NEVER HEARD (from a reputable source), NEVER READ, OR NEVER SEEN ANY ANALYSIS, that says they need 'DOWN TIME'....And there is PLENTY of research that says they veg faster with 24 hrs a day....Not to mention having done it both ways decades ago, and saw for myself, that they veg faster with 24hr.... It does save a few bucks on electric but photosynthesis CONTINUES with the lights on 24hrs a day....YT