Changing the Preferred Time server

Hi Team,

We have 7 win2k8r2- DCs.  Our PDC points to external Time Source and 4 DCs poiniting to the PDC for Time Source.  i used w32tm command to check this , but 2 DCs are not pointing to the another DC  (Non PDC ) for Time Source. Does this will create Problems and How can i change this...

Thanks SUBBU.T