When you register a new domain name, there's a technical process known as "propagation". This term refers to the transmission of data that takes place so that everyone knows your domain exists and is active.
This process depends on internet providers, who need to update their DNS records.
In general, the process is complete for 99% of internet connections within less than 2 hours, but the remaining 1% may take up to 72 hours.
So whenever you register or change the DNS of your domain, you're subject to the propagation of the new domain data across the internet.