Your questions: ‘If we installed the December 2007 Microsoft daylight saving time updates, are we covered for the changes this Fall?’

Recently, I received a question similar to one I answered last year on daylight saving time and time zone updates to Windows:

"We updated our systems earlier this year for daylight saving time [the rules for the US and Canada].  Is there anything we need to do?  Should we also update our systems with the last DST update? [referring to the August 2008 cumulative update]

Generally, the answer is yes.  As I noted earlier here, it depends.

See this blog post for a top-level look at the latest DST and TZ updates for Windows.  We also tell our customers that for some companies that don't have a presence in an affected time zone, no DST updates may be required. However, Microsoft strongly recommends that customers apply the time zone updates for all affected products. There are a couple of reasons for this:

  • First, customers may have users who travel to an affected time zone, and as such, their applications could be affected by not having the current time zone updates installed on their client machines.

  • Second, applying the current DST updates to all machines and applications keeps their environment up-to-date and consistent with worldwide changes. This could be important when communicating with another end user or company in an affected time zone, or where different IT environments come together and coexist.

Overall, Microsoft strongly recommends DST patch installation on all affected systems, devices and applications to ensure consistency with the world’s current time zone information.  Customers should review the updates available and posted at for the latest and updated information of Microsoft products affected by daylight saving time, as well as the main DST and TZ page at

Customers who need the latest updates for the recently-added and revised countries (including new time zone rules for Argentina, Morocco and Pakistan), should get the latest update.  Consumers may update their PCs by visiting Microsoft Update at Also, network managers and sysadmins should be able to get the latest Windows OS update as published this month (August 2008, KB 951072) as an "Update Rollup" via WSUS. See this past post illustrating the availability of the update from 2007. 

Technically, there are scenarios where updates and patches are not required, but Microsoft strongly recommends DST patch installation on all affected systems, devices and applications to ensure consistency with the world’s current time zone information.

Microsoft's product update schedule:  As I originally posted here, most Windows applications (and some services) reference the underlying OS for DST and time zone information, but some do not.  Microsoft Windows has established an annual update schedule (as outlined here); as noted in a prior post, many of our product teams are also following a similar annual product update cadence, with provisions for semi-annual as needed.  For each, the window closes for additional updates a few months (generally four to six) prior to the release date.  The regular Windows release provide a regular schedule for other product groups to follow.

Following the Windows regular cadence for publishing newly legislated DST rules and time zone updates, our "Cumulative DST and Time Zone Updates" will be released in November/ December (to the Download Centre and via Windows Update respectively) for the coming calendar year; when needed, we will also provide a semi-annual update in the July/August timeframe.  The group will also publish the new or modified TZI keys in an update to Microsoft KB article 914387 for IT professionals and sysadmins who may need that information.  We hope that this will provide a more predictable way for our customers to anticipate and plan for our scheduled product updates as they are published.

Implementing changes:  A note on making changes to daylight saving time and time zones: as officials consider changes to DST and time zone rules in their regions, in order to achieve more seamless transitions it is recommended that...  

  1. official confirmations of planned changes to DST and time zones, and

  2. ample advance communications and notice of the change be provided, along with concentrated efforts on promoting the change.  

Although such changes may be seen as a minor, local inconvenience (and not just for our customers in the impacted region but for enterprises around the world regardless of the systems in place), it is advised that long lead times be provided to implement these changes.  Ample advance notice and concentrated efforts on promoting any change should be provided to the people and businesses impacted.  In general, less than six months until such a change may not be enough time to get consumers, businesses and service providers alerted to the change.

Tags: Microsoft, Daylight Saving Time, Daylight Savings Time, DST. 3,410,000; 2,490,000 (up from 900K a year ago); 1,472,886

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