Setup Windows 2008 DC as an NTP Server

Run command as Administrator. On the DC you want to keep time:

net stop w32time
w32tm /unregister
w32tm /register
net start w32time
w32tm /config /manualpeerlist:0.us.pool.ntp.org,1.us.pool.ntp.org,2.us.pool.ntp.org,3.us.pool.ntp.org /syncfromflags:manual /reliable:yes /update

On your other DCs:

w32tm /config /manualpeerlist:FQDNofTimeKeeper /syncfromflags:manual /reliable:no /update