Setting a Domain Controller to Sync with External NTP Server

1. Modify Registry settings on the PDC Emulator for the forest root domain:
In this key:
HKLM\System\CurrentControlSet\Services\W32Time\Parameters\Type
• Change the Type REG_SZ value from NT5DS to NTP.
This determines from which peers W32Time will accept synchronization. When the REG_SZ value is changed from NT5DS to NTP, the PDC Emulator synchronizes from the list of
reliable time servers specified in the NtpServer registry key.
HKLM\SYSTEM\CurrentControlSet\Services\W32Time\Parameters\NtpServer
• Change the NtpServer value from time.windows.com,0x1 to ie.pool.ntp.org,0x1

This entry specifies a space-delimited list of stratum 1 timeservers from which the local computer can obtain reliable time stamps. The list can use either fully-qualified domain
names or IP addresses. (If DNS names are used, you must append ,0x1 to the end of each DNS name.) In this key:
HKLM\System\CurrentControlSet\Services\W32Time\Config
• Change AnnounceFlags REG_DWORD from 10 to 5. This entry controls whether the local computer is marked as a reliable time server (which is only possible if the previous registry entry is set to NTP as described above). Change the REG_DWORD value from 10 to 5 here.
2. Stop and restart the time service:
net stop w32time
net start w32time
3. Manually force an update:
w32tm /resync /rediscover
(Microsoft KB article # 816042 provides detailed instructions for this process.) Apart from that you can refer to this link as well.

As a thumb rule test this before applying for the production network. This is recommend if your organization preparing to move to 100% virtualization environment. If not at all cost try to have one DC in a physical server :)

Update: I found out Microsoft has already released an article about running Domain controller in HYPER-V. You can download the document from here.