Just a quick little reference for my own personal life.
Applies to server 2003-2008 R2 (and beyond most likely)
Follow instructions here from Microsoft for the GUI version!
Follow instructions here from Microsoft for the CLI version!
Make sure to modify the w32tm/ntp service too!
On the new DC:
w32tm /config /manualpeerlist:pool.ntp.org /syncfromflags:manual /reliable:yes /update
net stop w32time
net start w32time
On the old DC:
w32tm /config /syncfromflags:domhier /reliable:no /update
net stop w32time
net start w32time
Have a dance party on the old DC!