Golden Retrievers are usually very vigilant dogs and are sensitive to their owner or walker's pace. This is why they are popular breeds chosen to be guide dogs. You should find that your dog being a Golden Retriever will get the hang of walking on a leash quite a lot quicker than other breeds of dog.
If he is a puppy, training should take from a couple of weeks to around a month as long as you practice on his daily walks. If you are training an older dog that has had years of bad habits on a leash, these are going to be a lot harder to break. You will probably need a few months to correct these ingrained traits.
You will need a generous supply of tasty dog treats and his favorite toys. If he doesn’t have any toys yet, a good one would be a tug rope so that you can play tug and pull with him.