Question about change to my 12 & 12 light schedule ?

I'm growing 5 x Ak48 and they are in their 4th week of flowering (lights on at 8pm) and doing very nicely (if I do say so myself!). I have also taken 20 cuttings and they have all taken and now in their 1st week of veg. I'm lucky enough to have 2 lamps but my electric supply is not good enough to run a 400 & 600 HPS at the same time (keeps tripping my fuse box),and I can't fit all 25 plants under 1 lamp. So my thought is that I would run 1 lamp for 12 hours with my 5 flowering (4 weeks ish till harvest) and then run my other lamp for 12 hours (lights on 8am - 8pm) with the 20 smaller plants when the 1st lamp goes off. In 4 weeks when I harvest I want to move my 20 plants back to 12/12 (8pm - 8am). My question is; to do this I will either have to either give them 24hours of darkness or 24 hours of light to get them back on to a 8pm -8am lights on schedule. I'm thinking that 24 hours of darkness will be the better option but does anyone have any experience or advice to offer?? Thanks In advance, any advice greatly appreciated.

It might be a better long-term solution to look into fixing your electrical issues. Won't be as difficult as you think.

Why should you move your 20 plants to (8pm - 8am)? They are already on 12/12 cycle as I understand it. But if you want to do it, I would go for 24 hours of darkness.

ookami said:

Why should you move your 20 plants to (8pm - 8am)? They are already on 12/12 cycle as I understand it. But if you want to do it, I would go for 24 hours of darkness.

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This. Especially if you're just adding +12 hours darkness to a darkness cycle. 12 extra hours of darkness may shock the plant, but it will recover quickly. 12 extra hours of light will cause hormonal issues as the plant tries to revert back to a vegetative stage, and some strains are very very slow to transition back if they've been triggered to reveg. Unlikely to happen in ONE cycle, but you'd be starting the process, and we can't predict how quickly every strain will react. Some might have no issues, and some might get extremely stressed.

Thanks for the input. I prefer a 12 N 12 starting at 8pm for temperature reasons as I grow in the UK and find it easier to keep temperature more stable this way. Think I will go for an extra 12 hours of darkness to get back to my preferred on/off times. I've grown AK 48 before and its pretty tolerant.