Don't interuppt light cycles. You have to replicate the natural sun cycles. The sun does not turn "on" and "off" throughout the day, and cloud cover doesn't come close.

the numbers x/x (e.x: 18/6, 24/0, 12/12) are meant to be completed fully and in a consistent manner. 18 hours on, then 6 hours off.

I would recommend 18/6 for vegetative growing, 12/12 for flowering.