This is typically a problem caused by a firewall which prevents TweakMASTER from accessing the Internet on its own to check the time servers.
Most firewalls using NAT (Network Address Translation) behind a router pose no problems, however if yours does, please do the following: Create a firewall rule (as you do with any application that accesses the internet) to allow TweakMASTER manage its activities as needed.
If your clock is still failing to update from the time servers listed, you should configure your firewall to allow NTP to pass through, e.g. to open UDP port 123. If there is still some problem, you can try to enter a server address manually (preferably one that you know works ok).