Light cycle Question!

I just planted my plants and they are about 2 inches tall. I have a 400 W HPS light what do you recoment for light cycle? How many hours on how many off? And at what time do i switch to a different cycle?

I like 17/7 but most people would say 18/6 is best. But I like to have a good rooting system.

18 on 6 off. You wno't be switching it for awhile. By then you will have found out what to do. VV

thank you!!!!!!!!