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No, it's done at three days or younger. Fast forward to about 3:15:

As mentioned hatcheries vent sex and usually guarantee 90 to 95% accuracy. The hatcheries will also feather sex and color sex for the appropriate sex linked varieties. I would assume (yes, I know what they say about assuming) one of three options: the breeder doesn't know what she's doing...

If they're purebred Orpingtons, they shouldn't be feather sexable--that's a sex-link trait that requires specifically breeding a slow-feathering breed and a fast-feathering breed and the cross only works that first cross (just like black sex links, and red sex links).