How long does DNS propagation take to complete?
DNS propagation, the process of DNS updating to reflect newly entered values actually doesn’t have a set time frame. Each user on different ISP’s will pick up changes at different rates.
The TTL values, or Time To Live, on a domain advise how frequently the DNS should be checked for new records, but alas this guideline isn’t always followed. You will typically find DNS will refresh every 2-4 hours, but it could be as quickly as minutes or as long as 48 hours.
To learn more about how DNS functions, please view this video http://www.youtube.com/watch?v=72snZctFFtA