I've read this nice article from Gareth Hooper regarding Domain Controller syncing to external time sources. In essence, he wrote that although Microsoft don't actually condone the practice, it's a good idea to pre-configure all DCs (especially the ones that are most likely to get the PDC Emulator FSMO Role transferred to) to sync with an external time source and be marked as "Reliable".
Now, my question is:
We have one RODC in each branch location. If a locally reliable (external) time source is available for a branch, should I configure the RODC to sync to that time source? Or should I just cross my fingers and hope that time sync -- even if the WAN link to Head Office gets interrupted for a significant amount of time -- will somehow be maintained and/or restored with the DCs in Had Office?