By the time you read this, if it's asphalt, it will be fine to walk on. If it's concrete, it should also be fine. Concrete sets up quickly to a walkable surface within 24 hours. At that time it is still soft enough to damage easily by dropping something, say a large rock, on it, so take some care. At the end of 7 days, it will have reached 90% of the ultimate strength and hardness it will ever have.