Dns updating time
Now if you control all of the authorative DNS servers for a domain (that is, the DNS servers that actually host the zone files and can answers queries for the domain as opposed to having to ask another DNS server), then with the exception of how long negative responses should be cached, these settings may not seem as important since you can force the secondary servers to update whenever needed.
By if you are using third-party name servers which you do not control as your secondary name servers (such as Peer 1's Super DNS servers), then these settings are vitally important to how fast any changes are propagated.
Without DNS, that website you've worked so hard on would be completely invisible.
So let's go over each of these settings Fully-qualified domain name of the primary or master name server for the zone file.