It will start to flower at 12/12. Naturaly the days will die down to 12/12.
First off depends how old is your plant? And is there any pre flowers? You could force flower it by putting something dark over it. But be sure it isnt touching the plant. IE-Box, Bag. Let the plant get 12 hours light. Then put the bag over it. Say the sun rises at 7 am. Then at 7 pm put a bag over it. Hope This help's.


Cheers.