TTL stands for "time to live." It refers to the amount of time individual ISPs remember the current address to which your host name points. When your IP address changes, our name servers will instantly start referring requests to your new address. However, if an ISP has your address cached, users of that ISP may not be immediately pointed to the new address.
For example, if your host name has a TTL of 5 minutes and your IP address changes, and an ISP has already cached your host name's location, it may take up to 5 minutes before users of the ISP can access your computer's services via your host name. If your host has a TTL of 1 minute, it will only be 1 minute before your host is accessible again to those users. With a TTL of 0, your host will be available to everybody instantly.
Because some Internet Service Providers set their own minimum TTLs and ignore the requested TTL, it may take longer for some Internet users to access your host name than it takes others.