Faire partir une auto-floraison en 12/12

You shouldn't have any issues. But I would definitely bump up the light hours after your others are finished.

You can do it without any problem, but it will impact the size. The idea is to look at it in terms of hours to reach maturity, not days. For example, an autoflowering plant takes 60 days from seed. We're talking about 20h X 60 days = approximately 1200 hours to reach maturity. Generally, you can make up for the missed hours towards the end by switching to 12/12 to recover the lost hours. This is what I observed with some autoflowering WW that had been under 18/6. Once the number of days was reached, they were not fully mature, and we were able to extend it a bit (while closely monitoring your trichomes). However, it's certain that an autoflowering plant focuses on growth during the first 3 weeks. It continues to grow by about 30 to 50% during the next 2 weeks in pre-flowering. But if you reduce their lighting too much during the first 5 weeks, you will impact the base size of the plant, and therefore the final result.

Hey gardener! I think you can do it with autoflowers. I'm not an expert, but I saw that they need to be left under 18 hours of light. But like you said, they don't depend on light, so it shouldn't bother them. However, taking an extra 6 hours of light all of a sudden can be pretty harsh, so maybe it could stress them out. I really don't know, though. Good luck to you!