Sex linking works in a couple of ways - with red/black sex links, it is color sexing - for reds the pullets hatch reddish and cockerels hatch white; for blacks pullets have solid black heads and cockerels have a white/yellow dot on the head. These birds are produced by crossing color genes - for RSLs it is a red cock over a silver hen, for black it is a red cock over barred hens.
Feather sex linking is different - it is a careful cross of a slow feathering breed and a fast feathering breed (the slow feathering is related to a gene on the Z chromosome) - females of a slow feathering breed crossed to a male of a fast feathering breed will produce chicks that at 1-3 days of age (no older) with examination of the primaries and coverts on the wings and are differentiated with males feathering slow (like the mother) and females feathering fast (like the father)
Your birds, being RSL, would be sexed by color, not feathering.
