Description of how to set up an independent local NTP server on a Windows PC
Configuring an SNTP server in Windows 7
It's possible to configure Windows 7 to act as an SNTP server.
This guide should also work for Windows 10, the registry entries are identical.
First, stop the “Windows Time” service in “Services” (START > Control Panel > System and Security > Administrative Tools > Services).
Then open the registry editor (START > Run… > regedit), move to “HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\W32Time\TimeProviders\NtpServer” and set the “Enabled” value to 1.
Afterward, go to “HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\W32Time\Config” and set the “AnnounceFlags” value to 5.
Finally, start the “Windows Time” in “Services” and set the start type to “Automatic”.
If the firewall is enabled please add permission to Port 123 (UDP) or disable the firewall.
Be sure, that the service is started after the re-start of the PC.