There’s a great article on the Microsoft AD team blog about configuring the authoritative time server automatically via group policy and WMI filters. This may save you from domain time sync issues if your PDC emulator role eventually ends up moving to a different server.

http://blogs.technet.com/b/askds/archive/2008/11/13/configuring-an-authoritative-time-server-with-group-policy-using-wmi-filtering.aspx

Their article covers how to set up the WMI filter, but doesn’t address the settings for NTP. Those are listed in detail under this support note.

These are the settings I’ve implemented in my GPO using Admin Templates->System->Windows Time Service:

Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeConfig]
"MaxNegPhaseCorrection"=dword:00000708
"MaxPosPhaseCorrection"=dword:00000708
"AnnounceFlags"=dword:00000005
[HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeParameters]
"Type"="NTP"
"ntpserver"="au.pool.ntp.org,0x1"
[HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeTimeProvidersNtpClient]
"Enabled"=dword:00000001
"SpecialPollInterval"=dword:00000384
[HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesW32TimeTimeProvidersNtpServer]
"Enabled"=dword:00000001