but the f1 generation from an auto and a non auto parents will finish roughly 2 weeks earlier than the photosensitive strain on its own,so if it finished october 1st it would now finish around september 15th,with a few later and a few earlier,
Didn't know this, though it is good to know.
i think it takes at least 4 generations to produce a full auto from auto and non auto parents.
I don't think so.
If you were to cross an auto and non-auto the F1 offspring should all be auto heterozygotes (ie each F1 plant will carry one and only auto gene from its autoflowering parent; you need two to be autoflowering).
If you then crossed any two F1s to create an F2 generation, about 1/4 of those F2 plants will be expected to carry two autoflowering genes and be themselves autos.
So you really only need two generations of crosses to create SOME auto offspring from auto and non-auto parents.
Assuming you generated enough F2s to do the selection, you could then select out both an auto male and an auto female, and cross them to get 100% auto F3 offspring, etc.
At that point you've created an entirely new autoflowering hybrid line.
Now in practice, you probably wouldn't stop your breeding project there, since even though your new line should be 100% autoflowering (or nearly so), you still haven't stabilized any OTHER traits you were interested in when you started the project. Your F3 all auto plants would still throw off lots of different phenotypes.
If you want to do REAL breeding, you're either going to want to backcross your new autos with the non-autoflowering plant and repeat the cycle (requiring more selection to retain the autoflowering trait), or alternatively do your original F2 selections from LOTS of autoflowering plants, so you'd have plenty of male and female autos to choose from so you could select the absolutely best ones for further refinement.