I always use 24/0 for vegatative growth and 12/12 for the flowering cycle. Cannabis in vegatative growth does not require a dark period to rest from photosynthesis. Think of your plant growing outside. Pretty much getting 12 hours of lights a day. Now imagine that plant getting eternal sunshine. With 24/0 you can get two outdoor days in one day indoors. This will cut down your growing time by 50% compared to outdoor growing or by one and a half if you just did the 18/6.