Configure a Windows NTP Client for Network Clock Synchronization
The clocks of all servers on the vSphere network must be synchronized. You can configure a Windows NTP client as a source for clock synchronization on Windows servers.
Use the registry editor on the Windows server to make the configuration changes.
Procedure
1 Enable NTP mode.
a Go to the registry setting HKEY_LOCAL_MACHINE\ SYSTEM\ CurrentControlSet\ Services\ W32Time\ Parameters
b Set the Type value to NTP.
2 Enable the NTP client.
a Go to the registry setting HKEY_LOCAL_MACHINE\ SYSTEM\ CurrentControlSet\ Services\ W32Time\ Config
b Set the AnnounceFlags value to 5.
3 Enter the upstream NTP servers to synchronize from.
a Go to the registry setting HKEY_LOCAL_MACHINE\ SYSTEM\ CurrentControlSet\ Services\ W32Time\ TimeProviders.
b Set the NtpServer value to a list of at least three NTP servers.
For example, you might set the value to 0x1 1.pool.ntp.org,0x1 2.pool.ntp.org,0x1 3.pool.ntp.org.
4 Specify a 150-minute update interval.
a Go to the registry setting HKEY_LOCAL_MACHINE\ SYSTEM\ CurrentControlSet\ Services\W32Time\ TimeProviders\ NtpClient,
b Set the SpecialPollInterval value to 900.
5 Restart the W32time service for the changes to take effect.
From VMware blog