Argentina DST 2009/2010

Disclaimer:  The steps provided in this bulletin were created to mitigate the impacts that the daylight saving time changes may cause for customers in Argentina. These are the impacts primarily anticipated at the time this document was written, and the effects that customers may face are not restricted to them.  The suggested actions on this document might receive additional testing. The information described in this document may change without notice. In addition, customers should be aware that further guidance will be provided at any time by Microsoft.

Special notes: There is no official decree for the DST in Argentina yet, thus the information on this bulletin may change at any time.

Background – Argentina DST 2009/2010         

It is not clear or official as of October 16th 2009, what Argentina will be doing concerning the Daylight Saving time observation for 2009/2010.

In  December 2008, Microsoft implemented a Daylight Saving Time rule for the Windows Operating Systems which contains the following settings for the Argentinean time zone “(GMT -3:00) Buenos Aires”:

  • Daylight Saving Time starts at third Saturday of October at 11:59:59PM

  • Daylight Saving Time ends at second Saturday of March at 11:59:59PM

This bulletin was written considering 2 possible scenarios, as detailed below:

For provinces that will adopt the Daylight Saving Time in Argentina

There are no special instructions to transition to the daylight saving time (October 18th, 2009), for the following scenarios:

  • Machines that are updated with KB 955839 or KB 970653 available on Windows Update:

  • Machines adjusted according to the guidelines published on the Latam Blog last year.

Important notes:

  • If there is a need to update a Windows 2000 machine, customers may follow the procedures detailed in “How to manually update Windows Servers and Desktop Operating Systems” to update their systems as published on the Latam Blog last year.

  • Do not adjust the machine’s clock manually. This will cause adverse effects on your environment and it is not supported by Microsoft.

For provinces that will NOT adopt the Daylight Saving Time in Argentina

Per information on the Clarin newspaper, some Argentinean provinces will not adopt the daylight saving time as defined by the Federal government back in 2008.

The instruction for provinces that will not observe the DST in Argentina is “un-select” the DST setting "Automatically adjust clock for Daylight Saving Time" as displayed below:


Creating a script to “un-select” the “Automatically adjust clock for Daylight Saving Time” time zone setting on Windows Servers and desktop operating systems:

  1. Click Start, click Run, type notepad, and then click OK.

  2. Copy the following registry information, and then paste it into the Notepad document:

    Windows Registry Editor Version 5.00


  3. On the File menu, click Save As.

  4. Select a destination, and then type DSToff.reg in the File name box. 

  5. In the Save as type box, click All Files, and then click Save.

  6. Import this registry key on target machines by double clicking in the DSToff.reg and clicking ‘Yes’ when prompted. Execute this registry file in all machines (clients and servers) where you want to “un-select” the “Automatically adjust clock for Daylight Saving Time” setting.

  7. In order to deploy these time zone changes in a corporate environment, you can use a startup script as described below.

Deploying DST modifications using Group Policy

  1. Click Start, click Run, type notepad, and then press ENTER. 

  2. Copy the following code, and then paste it into the Notepad document.

    @echo off

    regedit /s \\\NETLOGON\DSToff.reg
    ver |find /i "6.0">nul
    IF %errorlevel% EQU 0 GOTO end


    Note:     You must replace the \\ notation above with the actual DNS domain name for your Active Directory domain.

  3. On the File menu, click Save As.

  4. DST2009Update.cmd in the File name box. 

  5. In the Save as type box, click All Files, and then click Save. 

  6. Copy the following files to the Netlogon share folder of the domain controller that holds the PDC emulator role in the domain:


  7. Wait until Active Directory replication occurs. Also, wait until the files and folders in the system volume (SYSVOL) shared folder replicate to domain controllers in the domain. 

  8. Click Start, click Run, type control admintools, and then click OK. 

  9. Double-click Active Directory Users and Computers

  10. Select an Organizational Unit (OU) which contains the computers that you want to apply this script to. In this example, we will use an OU that is named DST-COMPUTERS. This example also assumes that this OU contains computer accounts.

  11. Right-click the DST-COMPUTERS OU and then click Properties. 

  12. Click the Group Policy tab, click New, type DST Registry Update, and then press ENTER. 

  13. Click Edit. The Group Policy Object Editor tool starts.

  14. Expand Computer Configuration, expand Windows Settings, and then click Scripts (Startup/Shutdown). 

  15. Double-click Startup, and then click Add. 

  16. In the Script Name box, type the universal naming convention (UNC) path of the DST2009Update.cmd file that is located in the Netlogon share. For example, type \\\NETLOGON\DST2009Update.cmd. 

  17. Click OK two times. 

Note:     Client computers that are within the DST-COMPUTERS organizational unit will run the startup script the next time the machine starts up, meaning all machines needs to be restarted to be able to recognize the new DST configuration via Startup script.

Important information about procedures described in this section:

  • The instructions above can be applied on Windows 2000, Windows XP and Windows Server 2003 Operating systems. You may need to restart the machine for the changes to take effect.

  • The instructions above should not be used on Windows Vista or Windows Server 2008 operating systems. On these operating systems, please uncheck the “Automatically adjust clock for Daylight Saving Time” manually.

Impacts for Outlook clients and Exchange Servers

Please verify which of the options applies to your environment to determine the impact for Outlook clients and Exchange Servers:


For customers who will not experience a time zone configuration change

For customers who will not perform any modification on their current time zone configuration, we do not foresee any impact on the Outlook client and Exchange Server.

As a precautionary measure, we do recommend users to print their calendars before the start of the Daylight Saving time on Sunday, October 18th 2009, so they can have a printed reference.


For customers who will experience a time zone configuration change

Any modification on the operating system time zone configuration, such as un-selecting the checkbox "Automatically Adjust clock for Daylight Saving Time" will cause appointments on the Outlook client to be one hour off.

The appointments affected will likely be the ones created prior to any time zone change, which occur between October 18th 2009 and March 13th 2010.

Example of users who may experience issues with their Outlook calendar:

  • Users located in a province which adopted Daylight Saving Time in 2008, but will not observe a Daylight Saving Time in 2009.  Users in this province should “un-select” the DST setting “Automatically adjust clock for Daylight Saving Time” for the “(GMT -03:00) Buenos Aires” time zone.

What can I do to fix appointments affected by DST changes?

In case your Outlook calendar is affected by the DST changes, please manually modify each appointment on the affected months after the operating system time zone has been changed. 

We recommend you to print your calendar before any changes are made, and then review the calendar items to make sure these items appear at the correct times. You can use this printed copy of the calendar items as a reference.

How to manually modify Outlook calendar items?

  1. Start Outlook, and then open the Outlook calendar.

  2. Manually move each meeting that you organized so that they occur at the correct time. 

  3. Send an update for each meeting that you moved to the meeting attendees. This action causes the calendar for each attendee to display the correct time for the meeting. 

  4. Manually move each single-instance appointment.

  5. Manually move all recurring appointments affected by the changes. 

How to the Outlook issue could have been avoided?

  • Any change in the time zone for a country should be announced to the local companies months in advance prior to the change. This would give time for users and administrators to adapt to the new rules and would prevent users from creating appointments using the wrong time zone settings.

  • The provinces not following/adopting DST in Argentina this year should have communicated this decision at the end of the last DST period.

Comments (2)

  1. juancarlospaco says:

    Tienen que usar Linux como hacen con Microsoft Bing, asi de facil:

    sudo apt-get update ; sudo apt-get upgrade

  2. Kevin says:

    I created a DST GPO as instructed and it work partially.  The registry was updated and DST box was unchecked however the time never changed.  I tried rebooting several time with no luck.  I also ran net time /set /y… still no luck.  W32tm /resync failed as well.  I finally toggled the check box and finally the time changed.  Any help would be much appreciated.



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