A long time - couple months at least. Look up some threads on heeling - and what type of heeling do you want to teach? Formal, flashy, obedience heel? Or just informal heel? I'd start by getting the dog used to the basic position (left side), and giving you focus. Once that is rock solid, and the dog understands that the left side is a good place to be, and will give you good focus, start by luring the dog with food and take one step. It is a slow process. Takes time to get a good heel.