Windows Time gets accuracy improvements and leap second support

Martin Brinkmann
Jul 20, 2018
Windows, Windows 10

Microsoft plans to integrate improvements in  the upcoming Windows 10 version 1809 and Windows Server 2019 operating systems that improve the accuracy of time.

The upcoming versions of Windows include compliant leap second support, a new time synchronization protocol called Precision Time Protocol (PTP), software timestamping, clock source stability improvements, and traceability support.

Leap seconds are needed to keep UTC in-sync with mean solar time. Current regulation makes it necessary to adjust the time accordingly but also make sure to maintain accuracy during a leap second.

Leap seconds get added in a very specific way. A clock runs the seconds from 0 to 59 usually for a total of 60 seconds. Leap seconds add an extra second and this has to be reflected somehow. When a leap second occurs, it is added to the last minute of the UTC day; the clock goes from 0 to 60 which results in a total of 61 seconds being counted at the time.

Microsoft did even add support for negative leap seconds. While they never occurred before, Windows is prepared for the event that this is going to happen.

Negative leap seconds are counted in similar fashion, only that a second is removed and not added so that only 59 seconds are counted and not 60 as usually.

Microsoft made the decision to not use leap second smearing as an option. Leap second smearing refers to a technique in which the extra second is split into much smaller units and added to the time throughout the day.

The reason why the technique is not added is that it has an error of order +/- 0.5 seconds with respect to the definition of UTC.

Precision Time Protocol

The coming versions of Windows will include time accuracy improvements next to that. Microsoft plans to include the Precision Time Protocol in Windows Server 2019 (Windows 10 also? Microsoft does not say) which won't replace the current standard Network Time Protocol (NTP) but will be an option for industries that require more accurate time syncing between network devices.

The main issue with NTP is that it assumes that the round-trip delay is symmetric in the network. PTP on the other hand supports latency per device which is more accurate.

Enter Precision Time Protocol (IEEE 1588v2). PTP enables network devices to add the latency introduced by each network device into the timing measurements thereby providing a far more accurate time sample to the endpoint (Windows Server 2019 or Windows 10, host or virtual machine).

Software Timestamping

Another new concept that Microsoft will introduce in the coming versions of Windows is Software Timestamping.

Since timing packets need to be processed by the operating system's networking stack prior to being used by the time service, latency that is added by these processes need to be accounted for as well.

Latency introduced by the networking stack may add up to 200µs in extreme scenarios which alone is higher than the sub-100µs target of some government regulations.

Microsoft records the timestamp of packets before and after they have been processed by Windows Networking Components to make time more accurate.

Other improvements

Microsoft revealed one additional accuracy-based improvement and options to better trace accuracy:

Clock Source Stability 

Attempts to make the clock source more stable by changing how time samples are processed.

It’s important to understand that a host system receives time “samples” from its time server, however it does not immediately apply these samples to the clock.

[..] we take multiple time samples, eliminate the outliers, and discipline the clock with the goal of bringing the system closer and closer to synchronization with the time server.


Microsoft will add options to prove and trace the accuracy of time sources. Windows Server 2019 will include "additional logging capabilities  that can be used to audit the actions taken by the Windows Time service".

The logs may answer the following questions among others:

  • What is the chosen time server and synchronization frequency
  • When was the last synchronization and results of that synchronization
  • What actions were taken after the synchronization (did we discipline the clock?)

The operating system supports new performance counters and admins may use a SCOM management pack to get notifications when NTP Offset thresholds are exceeded. (via Deskmodder)

Windows Time gets accuracy improvements and leap second support
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Windows Time gets accuracy improvements and leap second support
Microsoft plans to integrate improvements in  the upcoming Windows 10 version 1809 and Windows Server 2019 operating systems that improve the accuracy of time.
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  1. Dan Donx said on January 15, 2023 at 10:29 am

    What mental age of reader are you targeting with the first sentence? 10?

    Why not write an article on how to *avoid* upgrading from W10 to W11. Analogous to those like me who avoided upgrading from 7 to 10 for as long as possible.

    If your paymaster Microsoft permits it, of course.

  2. Dexter said on January 15, 2023 at 11:14 am

    5. Rufus
    6. Ventoy

    PS. I hate reading these “SEO optimized” articles.

    1. cdr said on January 15, 2023 at 3:32 pm

      I used Rufus to create an installer for a 6th gen intel i5 that had MBR. It upgraded using Setup. No issues except for Win 11 always prompting me to replace my local account. Still using Win 10 Pro on all my other PCs to avoid the bullying.

  3. sv said on January 15, 2023 at 6:40 pm

    bit pointless to upgrade for the sake of upgrading as you never know when you’ll get locked out because ms might suddenly not provide updates to unsupported systems.

    ps…. time travelling?
    written. Jan 15, 2023
    Updated • Jan 13, 2023

    1. Martin Brinkmann said on January 16, 2023 at 5:49 am

      This happens when you schedule a post in WordPress and update it before setting the publication date.

  4. Anonymous said on January 16, 2023 at 8:24 am

    Anyone willing to downgrade to this awful OS must like inflicting themselves with harm.

  5. basingstoke said on January 16, 2023 at 11:18 am

    I have become convinced now that anybody who has no qualms with using Windows 11/10 must fit into one of the following brackets:

    1) Too young to remember a time before W10 and W11 (doesn’t know better)

    2) Wants to play the latest games on their PC above anything else (or deeply needs some software which already dropped W7 support)

    3) Doesn’t know too much about how computers work, worried that they’d be absolutely lost and in trouble without the “”latest security””

    4) Microsoft apologist that tries to justify that the latest “features” and “changes” are actually a good thing, that improve Windows

    5) Uses their computer to do a bare minimum of like 3 different things, browse web, check emails, etc, so really doesn’t fuss

    Obviously that doesn’t cover everyone, there’s also the category that:

    6) Actually liked W7 more than 10, and held out as long as possible before switching, begrudgingly uses 10 now

    Have I missed any group off this list?

    1. Heinz Strunk said on September 19, 2023 at 3:57 pm

      You have missed in this group just about any professional user that uses business software like CAD programs or ERP Programs which are 99% of all professional users from this list.

      Linux doesn’t help anyone who is not a linux kid and apple is just a fancy facebook machine.

  6. ilev said on August 24, 2023 at 7:34 pm

    Microsoft has removed KB5029351 update

    1. EP said on August 24, 2023 at 9:21 pm

      only from windows update though
      KB5029351 is still available from the ms update catalog site

  7. Anonymous said on August 24, 2023 at 11:05 pm

    1. This update is labaled as PREVIEW if it causes issues to unintelligent people, then they shouldn’t have allowed Preview updates ot install.

    2. I have installed it in a 11 years old computer, and no problems at all.

    3. Making a big drama over a bluescreen for an updated labeled as preview is ridiculous.

    This is probably another BS internet drama where people ran programs and scripts that modified the registry until they broke Windows, just for removing stuff that they weren’t even using just for the sake of it.
    Maybe people should stop playing geeks and actually either use Windows 10 or Windows 11, but don’t try to modify things just for the sake of it.

    Sometimes removing or stopping things (like defender is a perfect example) only need intelligence, not scripts or 3rd party programs that might mess with windows.

  8. john said on August 24, 2023 at 11:17 pm

    Windows 11 was a pointless release, it was just created because some of the Windows team wanted to boost sales with some sort of new and improved Windows 10. Instead, Microsoft cannot support one version well let alone two.

    1. John G. said on August 25, 2023 at 12:08 pm

      Windows 11 is the worst ugly shame by Microsoft ever. They should release with every new W11 version a complete free version of Starallback inside just to make this sh** OS functionally again.

  9. EP said on August 25, 2023 at 3:10 pm

    motherboard maker MSI has recently released a statement regarding the “unsupported processor” blue screen error for their boards using Intel 600/700 series chipsets & to avoid the KB5029351 Win11 update:–UNSUPPORTED-PROCESSOR–Error-Message-of-Windows-11-Update-KB5029351-Preview-142215

  10. EP said on August 29, 2023 at 7:32 pm

    check out the following recent articles:

    Neowin – Microsoft puts little blame on its Windows update after UNSUPPORTED PROCESSOR BSOD bug:

    BleepingComputer – Microsoft blames ‘unsupported processor’ blue screens on OEM vendors:

  11. Leonard Britvolli said on August 30, 2023 at 10:33 pm

    While there may be changes or updates to the Windows 10 Store for Business and Education in the future, it is premature to conclude that it will be discontinued based solely on rumors.

  12. sembrador said on September 5, 2023 at 9:32 pm

    My advice, I left win 15 years ago. Now I’m a happy linux user (linuxmint) but there is Centos, Fedora, Ubuntu depending on your needs.

  13. EP said on September 6, 2023 at 11:55 am

    motherboard maker MSI has recently released new BIOS/firmware updates for their Intel 600 & 700 series motherboards to fix the “UNSUPPORTED_PROCESSOR” problem (Sept. 6):–UNSUPPORTED-PROCESSOR–caused-BSOD-on-MSI-s-Intel-700-and-600-Series-Motherboards-142277

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