starting flowering under veg cycle?? Need help

i need some advicew. I need to start a 12/12 cycle on a few plants and clones i have, but i only have 1 grow room and 1 grow light, and i have another crop under the light in veg. can anyone give me some suggestions on how could i do the 12/12 under the same crop doing 18/6? i was thinking about just after 12 hours in the light cover the plants that i am going to flower with garbage bags, or anything else that will shield from light, maybe in corner of room. And uncover and put back with other crops after the 12 hrs dark. Can anyone help a dude out.

There's nothing stopping you from doing that, but you need to make sure that ALL the light is blocked from the plants in flower.

Also keep in mind that that is something you'd have to do EVERY day while your grow is going. I had to do babysitting bullsh!t like that with a past grow of mine, and I'll tell you it get real old real quick.

I like only having to check my plants out once every 2-3 days, instead of every day.

That will work for now, but once you have bud, mold maybe a problem with no air flow.

Also, if you mess up and forget for one day it can ruin it all.