It can take anywhere from 2 to 48 hours for any changes to propagate out to all of the DNS servers. Sometimes longer but very rarely does it take more than 24 hours.
One way to know if your setup is correct, is to change the DNS servers on your client computer to use the DNS servers you setup for your domain name. You may need to clear your browser cache and make sure that you are able to resolve the host name.
Still, you may have to wait if you are using Windows. This is because there are in effect two resolvers. It can still take several hours for Windows to re-fetch the updated DNS data. If you still see your old data, this does not mean that something is wrong. Be patient and check again later.
If, say in about 4-6 hours (actually you can do this now if you want), you are still not able to see your changes, then on a Linux computer use dig (there may be a dig for Windows too).
dig +trace example.com any
This will trace through the DNS servers looking for a SOA (statement of authority) DNS server and return the results. If you do not see your changes, then you likely did not make them on the right set of DNS servers. This happens a lot! You will be able to see what domain hosts your SOA which may likely be your registrar. It is not uncommon that a SOA is relatively blank if the name server NS records points to another set of DNS servers. This is not uncommon. This is often the case where the host and registrar are two separate companies. You would then be able to check using:
dig @ns1.hostingdomain.com example.com any
Please note that would be one of the domain names for the NS record. You can try both if you want, though this is often unnecessary.
This should get you what you want. Please let me know.