Try using dig to view the TTL of www.google.com
. or www.yahoo.com
. Both of them have CNAME records for www that have a certain TTL, and the CNAME resolves to several A records with even shorter TTLs. If you keep doing dig over and over again you will notice the TTL getting lower (as it expires from your nameserver's cache).
get a TTL of 300 for the A records from the CNAME of www.google.com
. and TTL of 60 for the A records resolved from the CNAME of www.yahoo.com
. (assuming it's not already cached).