Hi Bobster,
With the default settings 3DWatch looks every 2 seconds if an IP address has changed and updates the DNS service if so. The update process itself takes as long as a regular web access takes (e.g. below 1 second up to a few seconds).
There are no special settings to take care of. Of course you must enter your account data and select the corresponding DNS service. If 3DWatch is running behind a router you must select the Get IP address from a remote server checkbox. That's about it.
HTH
Thomas