DNS Propagation is a process in which worldwide DNS Servers queries the domain registrars to find updated information regarding DNS records of all newly registered or updated domain names. This process is repeated every few minutes to a few hours, and some DNS Servers fetch new or updated data after a few hours.
That is why it is said that the DNS propagation may take up to 48 hours to cover lately updated DNS Servers. If you have just updated your DNS records and want to check that the records are updated worldwide or not, then you are at the right place. Just enter the domain name and see what IP reflects against your domain name, and either it is your new server's IP or old server's IP.