How long do cartilage piercings hurt?

Since the question isn't too specific as to which cartilage you mean, I'm going to assume you mean the ear, since that is the most common.

Ear cartilage piercings don't usually hurt very long, but as with all piercings, it depends on the upkeep and care. It also depends on how quickly you personally heal. The problem with these piercings is that they can be in an inconvenient place, especially if you have long hair. When you brush your hair, be careful that you don't brush over them. Also, when you sleep, depending on where the earring is on your ear, it could poke into your head, and be uncomfortable. But you soon get used to it and learn how to position yourself to sleep more comfortably.

I have 12 earrings in each ear, and I love them. You just have to be very mindful of care, and sanitary habits when it comes to any piercings that you might have. :)