Indoor plant

I have a grow room, and growing some strawberry cough and big bud. Here's the thing, I know plants stress and start to flower at a 12/12 hour light cycle. But i want to know what if i grow my plants under a 18/6 light cycle for 2 months. Then thé 12/12 for 6-7weeks. Would my yield be big, like outdoor yields? Or would thé plants die.
 
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