One question plez about light cycle

I got 10 plants on a 18/6 cycle, 7 are now in there 4th week of veggie and seem ready to go into the 12/12 cycle, 3 of them are a different strain and only in there 3rd week of veggie and they seem to be growing alot slower then the other 7, I'm of course impatient and wanna start the 12/12 cycle for the others, but the 10 would be under the same light, SSSOOO can i start it? it seems like if i wait for the other 3 to show preflowers it would take at least 2 weeks, and i'm impatient, they are all under a 400 w metal halide bulb now and i will switch it to the HPS 400 W, and start the 12/12. If yeild or quality on the other 3 would be less then I will wait as long as need be, but if the only negative would be something like having to keep the 3 under the HPS longer, after the others are harvested, then that wouldn't be a problem. So reply plez!!!!
Soil, 400 w MH @ HPS, nutes, distilled water, 18/6, temp 78, humid 40-50, grow closet

any pictures??
how tall are the plants??
how many nodes do the plants have??

Im not sure how to respond to questions on this site so hope this works, so the 7 are at least a foot tall and at nodes 9 and 10, the 3 smaller ones are about 8 inches tall and at nodes 4 and 5, in the pics the smaller ones are in the middle, thx for responding fast

it's a hard call the foot tall plants are ready to flower as they will grow 2-3 times the foot they already are(3.5 foot).as for the other three you really want more nodes but personally i would just do them all now to avoid complication and if you have ten plants expect 4-5 females(unless you have feminised seeds) and the females will hopefully be the bigger plants.you got nothing to lose.

check out this thread i posted it may help you.
https://www.rollitup.org/general-marijuana-growing/120799-can-i-12-12-a.html

Thxs Luda i got nothing to lose i really liked that line.... and i'm gonna switch it tonight,

good let me know how you get on because i have some plants at a similar stage on 18/6 but i am still deciding if i should go 12/12 as they only have six nodes.
good luck.any questions just send a personal message i will get back a.s.a.p.
just click on my name and it gives you the option.if you look at the link i sent you will learn a lot of good pro's and con's.
and see me getting my ass whooped.