In Windows 7, you could get to the "Internet Time" settings by following the instructions in this Super User answer.
Now, I can get to this interface, but there is no option to set a custom NTP server or even see the current NTP server:
I want to get to this dialog box:
Where are "Internet Time Settings" in Windows 10?
Best Answer
"Internet Time Settings" dialog box
Registry key
You can still modify the default server registry key at
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\DateTime\Servers
to set a custom NTP server.