http://www.articlesbase.com/networks-articles/how-to-configure-windows-server-as-a-ntp-server-108481.html
This article describes how to make one of your servers a time server and you can then change the TimeServer setting from the windows clock to this server. The key steps are.
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeConfigAnnounceFlags
Set the ‘Announce Flags’ registry entry to 5, to indicate a reliable time source.
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeTimeProvidersNTPClientSpecialPollInterval
The ‘Special Poll Interval’ registry entry defines the period in seconds that the Windows 2003 machine should poll the NTP server. A recommended value is 900 seconds, which equates to every 15 minutes.
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeParametersNtpServer
The ‘NTP Server’ parameter is used to provide a list of IP addresses or DNS names, separated by a space, of NTP servers that the Windows 2003 machine can synchronise to.
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeTimeProvidersNTPServerEnabled
Changing the ‘Enabled’ flag to the value 1 enables the NTP Server.
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeParametersType
Change the server type to NTP by specifying ‘NTP’ in the ‘Type’ registry entry