If hatch day was Wednesday, it's already too late to try to feather sex sfh. First three days only, so I'm told.
True. I did the observation for the feather sexing pretty much as soon as they were born. I only had 3 chicks (all black Americauna or EE) with all the same length Primaries. All the others had long-short-long-short Primaries. I put a dot of white paint on the heads of the ones with the same length Primaries just as an experiment. I know as dhetzle said this will probably not work; but no harm experimenting.
I have about 90% accuracy on feather sexing if done within hours after hatching,
Good luck on the genetics, even after all these years, I just do not get it....so glad others do, so I can just ask.