At one week, the snood bud may be bigger in a tom.
At three weeks males may start strutting. (sometimes less)
At five weeks, neck feathers either start on the head (hen) or fewer on a tom
At eight weeks, true colors start coming in so color sexable birds like Narragansett and Blue Slate may show toms as darker feathered and hens as lighter feathered.
I am hatching numbers of turkeys and tracking each one with guess at hatch as to male or female based on primary/covert feather length. They do definitely differ, but most of my birds are too young yet to positively ID.