Switching to bloom nutes and photoperiod changes?

I don't start bloom nutes until after the stretch. This usually takes place 1-2 weeks after an auto first show calyxes. You'll recognize it when your plant doubles in size (or better) in one week. I personally prefer an 18/6 schedule, I think the plant benefits from dark period. This is highly debated though, and if you want to go the 24/0 route, just increase her light by a half hour every day until you hit 24 hours. Autos have ruderalis which is accustomed to 24 hours of light in it's natural habitat, so you won't hurt her. Honestly, you could probably just go right to 24 and not notice any I'll effects, but I think you can avoid shocking her if you ease her into it.