The very earliest I have seen them easily noticeable but not usually was 10 weeks. They will start to show on most birds clearly around 12 weeks, with some being later bloomers even as late as 16+ weeks. Certain breeds like Seabright and Campine (maybe more) have hen feathered males and will never get the pointy saddles. Silkies actually do get them as longer flowing saddles though not technically pointed.. still pretty clearly if you have a female for comparison.
Sometimes it is more challenging to discern if you are actually seeing pointed feathers when they are laced or patterned breeds because the lacing can look pointy itself. However, in laced breeds the male saddle feathers will be solid color, different than the rest of the body.
Now in the solid colors it can be challenging if they have very messed up tail feathers.. either from flock antics, parasites, recent predator attack, or just being in a really awkward phase of growth. Those ones sometimes throw even more experienced lookers for a loop. And shiny green iridescence (on black birds) is not usually an indicator of gender. But shiny bright red iridescence in feathers is, especially around the wing shoulder and saddle areas. Females can get red leakage but it's usually much more muted brownish than what I might call shiny almost orange on the ones that do get that color.
Please note that while these statements are basically true.. there seems to always be an exception to most every rule... Hens DO get pointed saddle feathers.. if they've had reproductive weirdness happen. I've witnessed a two year old hen crow and plenty of roosters get startled and/or join in to sing the egg song! INfertile eggs can sometimes develop slightly despite never being able to hatch. The ONLY rule I've yet to see broken.. Is Roosters don't lay eggs!
Hope this is useful as well as entertaining!
