Auto 20 days slow growth

Yes. You can grow them under 12/12 from seed, its gonna be smaller but it doesn't really matter because you are taking advantage of the gaps without plants that are just a waste of light. Autoflowers will flower under 12/12 without issues, they will also flower basically under any other light schedule, if it doesn't then it isn't an auto, and don't switch from 16/8 to 12/12 unless you already got other photos nearby that need that light schedule switch, but other than that there's no benefit in reducing the light of an auto like if it was a photodependent strain. If an autoflower does not flower, you must switch her to 12/12, if you have her under 12/12 already then you have a 99,99% that she will flower at some point, some autos start flower at 3rd week, others at 6th, you just never know for sure untill ur growing it. Stay lit growmie.