How long does it take to evolve an egg in Pokemon

It's not the amount of time taken, but the amount of steps which varies from species to species. Generally it can be around 4000 steps, but the exact number depends on which Pokemon you are attempting to hatch. Some are more, some are less. Generally the rareness of the Pokemon is some indication of how long it will take, rarer taking longer. Remember that standing still will have no effect on hatching, so just keep moving--if you can get to a cycle path it will be a lot easier on your fingers, but most breeders have a special route of choice.