Sadly it all depends. I am 2 months on T, and I have already seen significant darkening of my mustache, and I have to shave every other day. The hair on my chin is rough and thick but not dark yet, except for one lonely dark hair lol. Lots of things come in to play when you're talking about changes. Your starting dose, your ideal dose, what dose you're on right now, your genetics, your diet and habits, your hairiness before starting T... All of those things change how fast you'll see changes and how much change there will be.