Can you help me understand this? I registered a domain name at 2am and linked it to my hosting. I added some markup to the index.html file using FileZilla, but nothing seems to be happening.

After reaching out to the support team from where I bought the domain, they responded by saying that I need to wait for the DNS servers to update. This process takes up to a day or sometimes more and is dependent on my internet provider's servers. Although most sources online say that the maximum wait time is 3-6 hours, some providers may take up to 72 hours to update their DNS servers.

Have you ever encountered this issue? Do you have any suggestions on what I might be doing wrong?

Updating DNS records on all servers at once is not possible, but this should not be concerning. Opt for the registrar DNS and your website will likely be accessible within a few minutes of changes being made. You can use the nslookup tool to check the status of your DNS records through various DNS servers including Google's 8.8.8.8. Additionally, you can access third-party whois services to verify the correctness of your DNS records and obtain additional information about your domain name. However, it may not tell you if your site is accessible from your current provider.

Referring to the RFC, the maximum waiting time for DNS updates is 86400 seconds or 24 hours. After this period, all devices should discard the previous DNS record and replace it with a new one.

If you visited the address before changing the NS, then you may have accessed the cached records from your provider. To ensure that the changes are reflected, it's best to wait for 24 hours. However, if you made the changes without accessing the address first, then everything should open in a couple of minutes.

For more information on how DNS works, I recommend checking out https://howdns.works/.