Can you clarify your question? If you are asking how long a new record takes to propagate out to remote DNS servers, you can find out by asking each DNS server.
On Windows, from a cmd prompt, or in Terminal.app on Mac, or a terminal window in Linux:
nslookup my-new-record.domain.com dns-server.internet.com
You can also look up more information on a command line utility called dig. Here's a web interface for dig:
If you're asking how long a DNS record lasts before getting deleted or updated, that's the TTL (time to live) field in a DNS response.
Open the link above
type in nstld.verisign-grs.com for the hostname
change the Type to A
click on Dig
the second field in the response is 300, which means this record has a time-to-live of 300 seconds. Any cached responses for this record will check the authoritative server for updates after the TTL expires.