To the first question, you can uncheck to the "Synchronize with an Internet time server" so Windows uses the BIOS clock time. There was an old answer about setting the BIOS to UTC time when using a write filter, but I cannot seem to find it at the moment.
The second question is something you will have to develop. Since internet time sync is off, you will have to create a service that detects internet / intranet connection to get the time and update the BIOS clock.
Are you looking to connect to a different time source on the network?