The domain record data is not stored on one single server. The information is spread throughout millions of services all around the world. This Domain Name System (DNS) allows you to find out where a domain name points and access the server it points to.
Because this data is replicated around the world on millions of servers, whenever you make changes to the master record through your registrar or to the zone record on our server, the changes need to be transferred to all the servers.
The servers do not check for updates every second as this would produce too much traffic. Most are setup to discard their records every 24 hours and if the domain is requested with no record, it will lookup a new copy. On that new copy will be any updates you performed.
Other servers may have their update time set to lower or higher, but usually no higher than 72 hours. As such, it can take up to 72 hours for the entire world to reflect any changes.