To synchronize the time on your computer with one of the NTP server IEN...

you must follow the following steps from the "command prompt":

net time /SETSNTP:time.ien.it
net stop w32time
net start w32time

You can also configure the PC as "Authoritative Time Server", in this case, run the application regedit.exe and select the following key:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\Parameters]

edit or create (if doesn't exist) the following value:

"LocalNTP"=dword:1

restart the service "Windows Time":

net stop w32time
net start w32time

in this way the computer just set can be used as NTP server.