German Shorthaired Pointer Q&A
You can see evidence of where their ticking will be almost as soon as they are dry after birth. The skin underneath the white hair will be colored more darkly in the areas that will have ticking. Over the first couple of weeks after birth it will continue to be more obvious.
Usually around 4-6 weeks. Depending on color. Maybe a brown ticked pointer would show marking a week earlier than the blacks.