TTL for NS Record
Checks the TTL (Time to Live) for the name server DNS record.
The NS record for a domain name specifies which name servers are authoritative for that domain. The TTL (Time to Live) number instructs recursive name servers that they are allowed to cache this information for a certain amount of time, after which they should look up the information again. If the recursive name server has the information cached, then the lookup happens quickly and the user can load the website quickly. If the recursive name server has to look up the information, then there is a delay while this happens and the website will load a tiny bit slower. Therefore, for performance reasons, it is recommended to have the TTL be as long as practical for your particular server environment so that the recursive name servers can cache this information longer.
It is rare and unlikely that you would need to update your name servers in an emergency situation, so having very short TTLs should be unnecessary. This test will report an error if the TTL for the NS record is less than 5 minutes and it will provide a warning if it is less than 1 hour. There is also a danger to having the TTL be too long because this could prevent you from efficiently migrating your website to a new platform. This test will report an error if the TTL is longer than 1 week. We recommend setting the TTL to 1 day and then if you are planning a migration, you can update the TTL at least 1 day ahead of time to a lower value.
For very large and popular websites, the recursive name servers will almost always have the data cached, even with short TTLs, so this test becomes less important for large websites and there may be legitimate scenarios where short TTLs are important for large high-availability websites.