On 18/05/07, Blair Harrison
The .nz DNS zone push occurs at the following times each day 3am, 7 am, 11am, 3pm, 7pm, and 11pm.
So, any updates you do to nameservers will take effect after the next zone push.
The zone push actually happens on the hour, every hour (source: http://www.dnc.org.nz/story/30094-31-1.html#zone) Remember however that the .nz zone has a TTL of 1 hour (3600s), so even though you have made a change to your authoritative nameservers, it may take up to one hour after the zone push for all recursive nameservers to see the change.
Provided your registrar is communicating correctly with the SRS, the info should be updated in the whois pretty much instantaneously. If there's a problem with the SRS for whatever reason, then the update may be delayed.
Correct. Whois information is live, so any change made with your registrar is visible instantly. -- simon