The Hyper-V Time Synchronization service is one of the standard integration services available to a virtual machine. Within a Windows guest it appears as the Hyper-V Time Synchronization Service, with the service name vmictimesync.

It allows the Hyper-V host to influence the guest clock independently of Windows Time Service. This can be useful when a guest starts, resumes or recovers with a badly incorrect clock, but ongoing host synchronisation may be unnecessary where the guest already has a reliable Windows time source.

Domain members

A domain member running on Hyper-V should normally obtain time through Active Directory, in exactly the same way as a physical domain member.

Leaving Hyper-V Time Synchronization enabled means the host can also adjust the guest clock. Where the host and domain hierarchy agree, this may never produce a visible problem. If they differ, however, it becomes harder to establish which system is responsible for a correction or unexpected time change.

The preferred approach is therefore to disable the Time Synchronization integration service for domain-joined Windows guests and verify that the guest reports a domain controller as its Windows Time source.

w32tm /query /source
w32tm /query /status

Domain controllers

Microsoft recommends disabling host-to-guest time synchronisation for virtual domain controllers so that they follow the Active Directory time hierarchy instead.

The forest root PDC Emulator should use its approved external peers. Other domain controllers should use the domain hierarchy. Allowing the Hyper-V host to act as another source can undermine that design and may cause repeated clock changes.

This is particularly important because domain controller operations, Kerberos authentication and replication all depend on predictable time behaviour.

Standalone Windows guests

A standalone Windows guest has no domain hierarchy. It can use a manually configured NTP source through Windows Time Service or rely on the Hyper-V host.

Using Windows Time Service with several suitable NTP peers usually provides the clearest configuration because the source can be checked from within the guest and remains independent of the VM's current host.

Where a standalone guest is expected to move between Hyper-V hosts, relying only on host time also means the quality of its source can change after migration.

Disable Time Synchronization in Hyper-V Manager

To disable the integration service through Hyper-V Manager:

  1. Shut down the virtual machine if required by the host version and management workflow.
  2. Open the virtual machine's Settings.
  3. Select Integration Services.
  4. Clear Time synchronization.
  5. Start the virtual machine and verify its Windows Time source.

Disable Time Synchronization with PowerShell

Display the integration services for a virtual machine:

Get-VMIntegrationService -VMName "SERVER01"

Disable the Time Synchronization service:

Disable-VMIntegrationService -VMName "SERVER01" -Name "Time Synchronization"

Confirm the result:

Get-VMIntegrationService -VMName "SERVER01" -Name "Time Synchronization"

The display name can be localised on non-English hosts. Where this causes a problem, obtain the relevant integration service object with Get-VMIntegrationService and pass that object to Disable-VMIntegrationService.

Do not disable the guest service alone

The integration service can be controlled from the Hyper-V host or through the matching service inside the Windows guest.

Host-side configuration is normally clearer because it records the intended behaviour with the VM. If the integration service remains enabled on the host, Hyper-V may start the corresponding guest service again. Disabling it only inside Windows can therefore create an inconsistent configuration.

The Hyper-V host still needs accurate time

Disabling ongoing host synchronisation does not remove the need to configure the Hyper-V host correctly.

New guests can begin with the host clock, and correction may also occur around startup, saved-state restoration or recovery events depending on the operating system and platform behaviour. A badly incorrect host can therefore affect a VM before Windows Time Service has selected its normal source.

Standalone Hyper-V hosts should use reliable NTP peers. Domain-joined Hyper-V hosts should normally follow the domain hierarchy like other domain members.

Saved states, checkpoints and resume

A VM restored from a saved state or an older checkpoint may resume with a clock that is significantly behind the current time.

Microsoft's Windows Time documentation describes partially disabling host synchronisation for virtual domain controllers so that the domain hierarchy remains authoritative while the platform can still protect against large skew after a saved-state restoration. The precise behaviour has changed across Windows and Hyper-V versions, so recovery procedures should include an explicit time check.

After restoring or resuming a Windows guest, run:

w32tm /query /source
w32tm /query /status
w32tm /resync /rediscover

Do not assume that the source shown before the checkpoint remains valid afterwards.

Checking the guest

Where Hyper-V integration is influencing the guest, Windows may report:

VM IC Time Synchronization Provider

For a domain member configured to use Active Directory, the expected source is normally a domain controller instead.

The complete effective configuration can be displayed with:

w32tm /query /configuration

Check that the synchronisation type is appropriate for the guest: normally NT5DS for a domain member and NTP for a standalone server using manual peers.

Common mistakes

  • Disabling Hyper-V Time Synchronization without configuring Windows Time Service correctly.
  • Assuming the Hyper-V host clock no longer matters after guest synchronisation is disabled.
  • Allowing a virtual domain controller to use both the host and the domain hierarchy.
  • Stopping vmictimesync in the guest while leaving the integration service enabled on the host.
  • Restoring an old checkpoint and not verifying the guest clock afterwards.
  • Checking the configured peer list but not the source currently selected by Windows.

Microsoft documentation

Related information