Changes of authoritative nameservers apply within: 48hrs
If you change your Authoritative Nameservers in domains.ng account, this change can take up to 48 hours to fully propagate across the Internet. However, we immediately submit any such changes you make to the registry, but after that, it’s pretty much out of our hands.
To check the Authoritative Nameserver propagation, you can use a DNS propagation checker such as https://www.whatsmydns.net/ and select “NS” as the record type.