XXXXXXXXXXXXX is not advertising as a time server
The above is displayed in BDC's dcdiag result. So, I try to fix the issue by googling and get this solution finally.
net stop w32time
w32tm /config /manualpeerlist:peers /syncfromflags:DOMHIER /update
net start w32time
w32tm /resync
w32tm /config /manualpeerlist:peers /syncfromflags:DOMHIER /update
net start w32time
w32tm /resync
Ref: grinch2171 (http://www.ozzu.com/mswindows-forum/how-configure-ntp-server-windows-2003-server-t91197.html)