How to sync NTP server to windows source using SWG 5.2

Hi,

I have a NTP server in my environment and i would like to sync it to time.nist.gov, i have synced SWG 5.2 to time.nist.gov 

Now since i have SWG conenct to time.nist.gov should i  create a policy to allow the windows source NTP for a particular group or is it enough to just configure the proxy and the internal NTP server will udpate the time from SWG where as SWG will update it from windows source NTP server, how is it?