The maturity rate at which a cockerel starts to feather out with its mature phenotype will vary from one bird to the other one, even hatch mates, it has nothing to do with the e allele mutation.But wild type and wheaten birds feather in differently with their first set of feathers. Way before any thing close to maturity.
Color Sexual Dimorphism is related to the synthesis/Conversion of Androgen(for Roosters) to Estrogen(for hens) at the Skin level. The Henny feathering basically transform the rooster's normal Androgen activity at the skin level to Estrogen and that causes female feather.
Similar results can be obtained if one applies Androgen to roosters skin for example on this study: Variation in Plumage Response of Brown Leghorn Capons to Oestrone https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.1935.0050
And Females when their ovaries are damaged they start to transition to a pseudo rooster state, their skin no longer start synthetizing Estrogen but Androgen, they will produce male like feather pattern: https://www.livescience.com/13514-sex-change-chicken-gertie-hen-bertie-cockerel.html