(That's where the TTL (Time To Live) for the IP address matters - if it's set to a long time, the DNS server probably won't refresh till the TTL is up. If it's too short, that can cause other problems.)
Keef, have to pull you up on this - TTL has nothing whatsoever to do with DNS.
TTL is simply the number of gateways an IP packet can pass through before it is discarded. Each gateway decrements the TTL number in the IP packet header by one, until it reaches zero - at which point it is discarded. This was introduced into the IP spec. way back (I forget which RFC covers it) to avoid packets entering infinite loops.
SD