Time Synchronization on Virtual Domain Controllers

I have a 2012 Domain Controllers that are both Hyper V guests and want to confirm best practice for time sync.I KNOW this has been asked multiple times, but just want to make sure I am using the best practice.

What seems to make the most sense is on the DCs.

Leave the guest services enabled.  

Set the reg key below so that the Primary DC will get time from host on boot up
reg add HKLM\SYSTEM\CurrentControlSet\Services\W32Time\TimeProviders\VMICTimeProvider /v Enabled /t reg_dword

Set the Primary DC to get time sync from external source... such as pool.ntp.org

For other DCs, set to query primary

Then what to do with the physical host:

When it reboots where does it get its time?  Set to External?

Thanks for helping me figure out what is the best way to approach.