I started grit when I started them on things that were non-chick feed (they still get their starter feed). I give them spinach, meal worms, etc. as treats, so that's when they need the grit. I just sprinkle it on top of their chick feed.
Also, on an unrelated note, nice to see a Bengals' fan. I am a huge fan, as well, and looking forward to a better end to next season.