Depends on the knife and how much you use it. I sharpened a Chicago Cutlery for my boss at work and it got a few months of light work use. It basically is like touching up on a lightly aggressive 1200 grit stone--a hairy(wouldn't say "fine"), shiny, even scratch pattern.. It can be the end-of-the-line for a tougher, more abused knife.
Knowing you, I am guessing you didn't get them a brand new Forschner, so if it's a laser in high-performing heat treat, I would consider a fine grit stone instead(Like a Rika 5k...tell Dave to order those too, I need one meself). I learned to sharpen by doing edge maintenance touch-ups on a stone, so it's a good way to go if they want to learn to do it.