My flowering tent is lights on from 5 a.m. to 5 p.m. I’d like to hear how some of you have changed your light on 12/12 schedule to say something like 10 hours different lights on lights off 12/12. WHILE IN FULL FLOWER WEEK 5… AAAAND GO. I understand that Photo period plants stay in flower as long as the dark period is 12 hours uninterrupted. How would you all do it, lights on extra 10 hrs. or lights off 22 hrs. I’m asking how you would make the change with one timer edit so lights are on from 3 p.m to 3 a.m. From 5 a.m to 5 p.m.?
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Just give it a long day or night, they won’t notice. 
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Geez @cannabissequoia , i wanted to hear what a poser would have done, I knew the answer…lmao
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I’d go with off extra as to not cause a revegging or hermie
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Agree with extra off. Or just flip it on them and do a little stress testing.
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Why do you want to do this?
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The plats won’t be effected as long as you don’t keep switching like a hyena and keep it set . repeated changes will def effect your plants stress levels some do ok some don’t.
good luck with your vision…
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Probably summer temp control. I run at night.
Best bet is leaving a long night. Don’t extend the daylight hours. But keep off an extra 12 and start your pm on schedule from there.
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Some new growers out there would have eventually asked. I do it every year to compliment our HVAC… I know to just keep it dark the extra time. Ever since i started growing with quality seeds, the extra dark hasn’t caused a problem so far.
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Fair enough. My hvac is so undependable that I just run how I see fit.
Cheers
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Because of the heat in my region, I leave the lights on during the period when the temperature is lower, which in this case is at night from 7pm and they stay on until 7am.
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Just put them in extra dark one time only. Your plants know the exact time when the light goes off and comes on.
They only hold enough nutrients and enzymes to get them through the dark period without suffering growth and stress problems. So a one off change is the least stress for a photo period plant.
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100%…absolutely and well written… I am going for a blue pheno hunt between 2 females and want to force cooler temps during lights out, midwest usa doesnt have cool nights after this coming Sunday…lol…Time for A.C. @Shadey
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Yeah ac is a godsend, it does raise the cost of producing dramatically, depending on how big the space you are cooling is.
Also if you are re cycling the air through the ac, if your grow room is pretty much sealed up, to keep the ac working less, you will probably need to add a co2 supplement during lights on.
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I did it last year. You need to wait a full 24 hours. I did 25 hours total darkness. Had no problems whatsoever. They did drink a lot so you need to make sure you feed them.
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I believe if you got good strong plants you won’t have any problems. I’ve been fighting timers and ghosts lights this round. After 24 hours your plant does not know the time schedule. I didn’t have bisexual plants it didn’t stress them out at all. They actually loved it.
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I use 12 on, 13 off until I get to the start time I want.
Never had them notice… No problemos. 
Cheers
G
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So long as you don’t interrupt the night cycle, you can give them either a long day or a long night, won’t make a huge difference either way. I would lean towards a long night just to save a few $.
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Change the timer when the plants least expect it to remind them who’s really in charge 
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