I don’t extend the lights so I can’t give you any answers from experience. I know you butcher your cockerels and sell your pullets, not sure what you do with your older hens. I butcher pullets and hens, some laying, some not, and even a broody a couple of times. You can learn a lot by butchering pullets and hens. If a hen is laying she has a lot of ova in different sizes growing big enough to become a yolk. Her internal egg making factory is swollen, moist and soft. If she is not laying the ova are tiny and that internal factory is pretty dried up. I don’t know how long it takes for them to go from barren to ready to lay mode. I don’t think it is going to happen overnight unless they are already a long way toward getting ready to lay.
Length of daylight is not the only trigger to get them to start laying but it is a huge one. Some hens are going to lay in cold weather better than others. How much they eat, not just protein but other nutrients, can have an effect. Protein is a big one though. With shorter days they don’t have enough time to eat and digest as much as if the days were a bit longer.
My suggestion is to bite the bullet and try it. Now. Do whatever you are going to do and see when you start getting enough fertile eggs. Then adjust next year based on this year’s results. There will probably be some trial and error before you find your sweet spot.