You should veg (18 hrs a day of light) for 4-6 weeks before you cut back to 12hrs of light a day for flowering. Once you cut back you should see flowers 2-3 weeks later. Do not interrupt the dark cycle once you go to 12/12. This will cause hermaphrodites.

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Anything I say here is purely fictional. I do not use, or condone the use of illegal substances.