Typically, it takes a few hours or less. The time will depend on how fast your ISP updates DNS. When a new domain is registered or when DNS for a domain is changed, a set of master databases is updated with the information. After that, each ISP around the world will update records from the master database at an interval they choose. In my experience, it usually takes a few minutes, however, it can take much longer than that depending on your ISP and local network configuration and how often DNS is updated in your location.
So, that is why there is not really a set time and you just need to wait for the updated settings to propagate throughout the internet. It shouldn't take too long though!