Originally Posted by farmergiles

I would go for at least 18hrs light 6hrs dark for veg, some strains might start to flower with any less hrs light. You might as well just leave the lights on all the time for vegging IMO, hemp is slightly unusual in that it doesn`t mind continual light.

12hrs light 12 hrs darkness is normal for flowering. Sometimes it is useful to go to a light schedule with less than 12 hrs of light in a 24 hr period- this technique is used with some strains that have a tendency to veg indefinitely.

You don`t have to stick with a 24 hr time period but things might get confusing otherwise, both for the plant and you.

600w is fine for 6-12 plants.