A lot of people veg on 18/6. Are you sure they are flowering? Is it possible they are auto flowering plants?
From seed. Lst from veg. 2 plants in 2 gallon pot. 18 light 6 dark for veg. Same pot for flowering. But I switched to 18 light and 6 dark. I am experimenting with forced flowering and I have 14 main bud sites. All usin scrog method.