Windows Time Service

Stop the W32Time service:

net stop w32time

Configure the external time sources:

w32tm /config /syncfromflags:manual /manualpeerlist:”0.pool.ntp.org, 1.pool.ntp.org, 2.pool.ntp.org”

Make your PDC a reliable time source for the clients:

w32tm /config /reliable:yes

Start the w32time service:

net start w32time

The windows time service should begin synchronizing the time.

Check the external NTP servers in the time configuration by typing:

w32tm /query /configuration

Reference

http://defaultreasoning.wordpress.com/2009/11/16/synchronize-time-with-external-ntp-server-on-windows-server-2008-r2/