24/0 for seedlings to root under flo blue light
18/6 under metal halide or flo blue spectrum light.
12/12 under high pressure sodium, flo red spectrum light.
12/12 is really the only one you'll get anyone to agree on, the rest are personal preferences on time.
some will say it is best to have both spectrum's till flower.i also agree it is better to have both.
then just the red spectrum for flowering.
hope that helps ya.