The itching should only last a few days until some of the hair grows back in. However, during those few days, the itching is rather intense and very bothersome for the pup. You can do the cortizone cream (if the dog is not licking the spot too) as mentioned above. Any over the counter kind is sufficient but make sure the dog does not digest it by licking it off.

I prefer to just use a regular household item such as petrolum jelly (vaseline) to moistureize the spot until the itching subsides. If they do lick you can try to put a piece of clothing on to act as a barrier or you can use a elizabethian collar for a few days. They are wonderful for keeping dogs from chewing but don't do much for itching.