Depends. Like any bruise, how long it hurts depends on how severe the initial trauma was. If it is extremely painful, or if you suffered a severe blow, you might want to get checked out just to make sure you didn't fracture one of the bones in your face.
Usu 1-3 days. Usu 1-3 days, a lot pain is associated w the initial swelling. That's why ice and Ibuprofen can help w swelling and pain.