Domain Propagation is the period of time, or delay, involved in sending your domain’s address information to all the other name servers in the world. Name servers intentionally keep track of addresses for domains in their memory for a specific period of time which is defined by the administrator of the name server. This speeds up the process of looking up an address for a domain name. Unfortunately this "cached" information also stays in the name servers when it has been changed at the source of the original information (the domain’s registrar).
Name servers refresh themselves from once an hour to once a day. Generally 2-3 days time is a good estimate when a domain’s DNS information is changed at the domain registrar, after which everyone in the world can see the change.