From LedHed's Wiki
When transferring or seizing the PDC Emulator role remember to set the correct Authoritative Time Source.
More details on how to do this here: Configure 2008 Server for an External Time Source
Reference
http://technet.microsoft.com/en-us/library/cc773013%28WS.10%29.aspx
http://technet.microsoft.com/en-us/library/ce8890cf-ef46-4931-8e4a-2fc5b4ddb047
http://technet.microsoft.com/en-us/library/cc738042
http://blogs.technet.com/b/bpuhl/archive/2005/12/08/415827.aspx
http://www.networkworld.com/community/node/42190
http://technet.microsoft.com/en-us/library/cc784800%28v=ws.10%29.aspx