I observe the body and if all moult well I see little point in prolonging an unnatural process any longer than needs be. I also think that more time on the wing around the loft unhampered by the dark to light regime can only be a good thing? I sent seven to the SNFC nat in September, all were good around the face and neck, some further in the wing than others but no issues at all. Our darkness ybs are paired up in jan with the rest of the old birds and rear a nest from the stock but I have spoken with a couple of fanciers who let them mature and dont let them rear a nest until 2yr olds and say their results/losses improve! I might try this at some point