Your questions: do we have to worry about the coming Leap Second when it comes to Microsoft Windows and other products?

Clip art from Microsoft Office OnlineAs I Tweeted today (no, really, I can stop any time) I saw a question today on the subject of the coming leap second, as noted in the MSN posted article, 2009 to arrive not a second too soon, from’s Joe Rao:

"Wait a second.

"The start of next year will be delayed by circumstances beyond everyone’s control. Time will stand still for one second on New Year’s Eve, as we ring in the New Year on that Wednesday night. As a result, you’ll have an extra second to celebrate because a "Leap Second" will be added to 2008 to let a lagging Earth catch up to super-accurate clocks.

"By international agreement, the world’s timekeepers, in order to keep their official atomic clocks in step with the world’s irregular but gradually slowing rotation, have decreed that a Leap Second be inserted between 2008 and 2009." 

So I heard last night and saw this question today…

One Leap second will be added at the end of this year.  I wonder whether it will have impact on Windows, SQL Server or other Microsoft System. It seems that our SystemTime structure will reject the 60 second, and FileTime will ignore the LeapSecond.

"KB article  Q909614: How the Windows Time service treats a leap second and Blog "Please Look before you Leap a second" seems indicate we have not need to worry about Leap Second."

Great end of the year question.

Besides counting down "3, 2, 1, 1… Happy New Year!" to ring in 2009 in a couple of days, you’ll find more documenting the impact of a leap second in Microsoft Knowledge Base (KB) article 909614, How the Windows Time service treats a leap second (as Michael Kaplan noted in his most excellent post). 

In short, W32Time does not account for a leap second being dependent on the NTP server. Most applications and services may be unaffected, but sysadmins and IT professionals should know that the leap second is not addressed until the next time sync following the official addition/ subtraction of the leap second.  Consumers really have nothing to worry about save questioning whether or not the time is accurate as broadcast during Dick Clark’s New Year’s Rockin’ Eve when the crystal ball drops in Times Square.

Info on syncing clocks to absolute time, please see KB 816042, How to configure an authoritative time server in Windows Server 2003, and KB 884776, How to configure the Windows Time service against a large time offset.

General information on the Windows Time Service is also available in the team blog at  More articles/ information in which you may be interested:

(Of interest: The concept of a leap second is actually in question, and an ITU working group is evaluating whether or not the process of adding/subtracting leap seconds should be discontinued.)

Anyone else have additional information, guidance they’d like to offer?  I’ll add to this post as it comes in.

Tags: Microsoft, Daylight Saving Time, Daylight Savings Time, leap second, DST.

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3 replies on “Your questions: do we have to worry about the coming Leap Second when it comes to Microsoft Windows and other products?”

In a leap year you add a day, in a leap second you should only add 1/365th of a second 🙂

It may be beneficial to just drop all these references to leaps, DST and zones and just move directly to Zulu universally and let our calendar drift until it’s all out of whack. 😉  

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