Question : Time for DNS Serves to be recognized

Hello Experts,
I am experiencing an issue with DNS.
Moved Locations to new site.   Had 3 servers, 2 Public DNS and 1 Public Web Server
Changed IP Address to new Subnet.     (exp>   63.x.x.x to 68.x.x.x)
Changed all DNS records to new IP address.
Notified the Registar of the Domain change and new IP address.

Anyone can ping the DNS address, however, cannot resolve, mail.name.org for example.
but can telnet:   xxx.xxx.xxx.xxx 25
When I do an NSlookup
mail.name.org
server. ns1.corp.name.org
address:  xx.xx.xx.x
DNS request timed out.
       time out was 2 seconds

QUESTION:   how long does it take for DNS Servers to be recognized on a new subnet ?

Answer : Time for DNS Serves to be recognized

If you do a whois lookup on your domain name, are the IP addresses for the name server showing as updated?

It normally take between 24/48hrs for registras updates to take effect.