When switching to flower should the first 12 hrs b...

IMO I usually flip when the light go out so basically I just extend the night period

Hello So the light schedule is totally up to you. If you live somewhere hot it can be good to do the dark hours during the daytime to save on cooling. But run your usual 20 hour schedule and then just change the timer to reflect the new schedule. If it ends up only getting 8 hours of darkness that first day of the change leading up to the 12/12 switch thats ok, (the 8 hour darkness is just an example). Basically just adjust the timer and you'll be good, but don't give it excess hours of darkness.👍

Imran my plants 5 am till 11pm then when I switch to 12/12 I reset the timer to 7 PM till 7am so they get an extra 8 hours of light at first

No it should not... when a marijuana plant receives no light for 24 hours, it 100% contracts.. it shrinks.. not a good thing. it is the opposite of growing. even if it shaved a day or two off vege-bloom hormonal balance shift, it almost certainly is more of a negative than anything -- and that idea is just a guess to start.

To me it would make no difference either way. As the change in hormones and levels wont happen in a 12 hour cycle. What I do find helps speed up the conversion/transition. Is to slowly drop ur hours per day for a 5-7 day period. Decreasing ur hours of light by a hour or 2 at a time until u reach 12 hours a day. Happy growing and stay lit fam.