How daylight saving time (DST) changes in 2007 affect time stamps in Office files

This information applies to people who live in the areas of the United States and Canada that observe daylight saving time (DST) and who require that accurate time is recorded when their Microsoft Office 2003 and 2007 Microsoft Office system documents are saved or modified. For example, changes to a document might need to be time stamped for legal purposes. This information might also apply to people in other countries and territories that observe "summer time," during which clocks are adjusted forward one hour in early spring and adjusted backward in autumn.

In this article


Downloads and support information

For information about the latest Windows time zone update and to download and install the latest cumulative update, see KB 933360: August 2007 cumulative time zone update for Microsoft Windows operating systems

 Note   If you use Windows Vista or have signed up for Microsoft Update to receive updates automatically, you may not be affected by the change in daylight saving time. If you want to confirm that your computer is not affected by the Windows time zone update, visit the Daylight Saving Time Help and Support Center and follow the steps in the Daylight Saving Time Update Guide.

For more information about how DST changes may affect other Microsoft products, visit the Daylight Saving Time Help and Support Center.

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Background information

In August 2005, the United States Congress passed the Energy Policy Act, which changes the start date and end date of DST as observed in the United States. Some additional countries/regions are following the U.S. change. As such, in 2007, DST starts on March 11, 2007, and ends on November 4, 2007 — resulting in a new DST period that is four weeks longer than previously observed. These dates are referred to in this article as the extended DST period.

Daylight saving time rules

1987 to 2006     DST began (shifted the time one hour forward) at 2 A.M. on the first Sunday in April and ended (shifted the time one hour back) at 2 A.M. on the last Sunday in October.

Starting in 2007     DST begins at 2 A.M. on the second Sunday in March (three or four weeks earlier than previously observed, depending on the year) and ends at 2 A.M. on the first Sunday in November (one week later than previously observed).

  • In 2007, DST is observed from March 11 through November 4, in areas of the United States and Canada that observe DST.

Updates to Microsoft Windows

New DST definitions are built into Windows Vista. However, earlier versions of the Microsoft Windows operating system need an update to accommodate the early end to standard time. This single update is global and includes changes for the United States and Canada. The update affects the following products:

  • Microsoft Windows XP Service Pack 2 (SP2)
  • Microsoft Windows Server 2003 Service Pack 2 (SP2)
  • Microsoft Windows Server 2003 Service Pack 1 (SP1)
  • Windows Embedded for Point of Service
  • Windows Fundamentals for Legacy PCs

This time zone update also includes changes for other related DST changes and time zone behavior and settings that start in 2007 or have taken place since these versions of Windows were originally released. For more information on supporting the DST changes in Windows operating systems, see KB 933360: August 2007 cumulative time zone update for Microsoft Windows operating systems

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How the change in DST in 2007 might affect your Office files

Upcoming changes to DST might affect the time stamps on the file properties and tracked changes in Microsoft Office programs, such as Word, Excel, PowerPoint, and Project.

The new DST dates might affect the time or date (if revised within an hour of 12:00 midnight) that is stamped in items that are created or modified during the extended-DST periods or previous extended-DST periods in the following items.

Time stamped item Description
"Date modified" in file properties Date and time a document was last saved
Tracked changes in Word and Excel Date and time a revision was made
Tracked changes in PowerPoint Date and time a comment was inserted
Time functions Functions based on time such as TODAY() in Excel

"Date created" and "Date modified" in a file's properties

Files that are created after you or your IT administrator apply the Windows time zone update display the correct date-created and date-modified time in the file's properties. To view the properties, in Windows Explorer, go to the document location, such as My Documents. Right-click the document icon, and then click Properties. If you signed up to get updates from Microsoft Update or Windows Update, you might have received the DST update automatically. For more information, see Microsoft Update. However, documents with time stamps in previous extended-DST periods (for example, between March 12, 2006 and April 2, 2006, as well as the week between October 29, 2006 and November 5, 2006) are also shifted by one hour.

Here is an example to show the impact on time stamps for a document that you created on March 20, 2006, and saved at 7:28 P.M. in a U.S. time zone that observes daylight saving time (see Figure 1).

Properties dialog box

Fig. 1  Before the Windows time zone update was applied.

After you apply the Windows update for DST 2007, the file that was created last year displays the incorrect time stamp in its date-created and date-modified properties of 8:28 P.M. (see Figure 2).

Properties dialog box

Fig. 2  After the Windows time zone update was applied.

Files that you create after applying the Windows operating system update for DST 2007 correctly display the time stamps. If you do not apply the Windows time zone update, the date-modified property of the document created in 2007 is not shifted during the new DST period and incorrectly displays 6:28 P.M. However, the displayed times of the document created in 2006 are not shifted either and display the correct time stamp of 7:28 P.M.

Document created on March 20    

Current year – 2007 Previous year - 2006
DST update applied Correct 7:28 P.M. Incorrect 8:28 P.M.
DST update not applied Incorrect 6:28 P.M. Correct 7:28 P.M.

Tracked changes and time functions

Time stamps in tracked changes and inserted comments in Microsoft Office Word, Microsoft Office Excel, and Microsoft Office PowerPoint are recorded based on your system clock in the Windows operating system.

  • To view the system clock in Category view, click Start, click Control Panel, click Date, Time, Language, and Regional Options, and then click Date and Time.
  • To view the system clock in Classic view, click Start, click Control Panel, and then click Date and Time.

When you apply the Windows time zone update, these time stamps display the correct time for items that are modified during the extended DST period. Additionally, no changes are made retroactively. Therefore, time stamps in previous extended-DST periods also are displayed correctly.

Time functions, such as TODAY() in Excel, are also based on the system clock in the Windows operating system.

Function Behavior When Windows is updated
Tracked changes in Microsoft Office Word Each tracked change is stamped with the current date and time. New comments correctly reflect the updated system time. Previous time stamps are not changed retroactively.
Tracked changes in Microsoft Office Excel Each tracked change is stamped with the current date and time. New comments correctly reflect the updated system time. Previous time stamps are not changed retroactively.
Time functions in Excel Functions such as TODAY() and NOW() use the system clock in the Windows operating system to determine the current date and time. When a change is made to the system clock, whether it is a change to the time zone or a change to or from daylight saving time, the function returns a value that is consistent with the updated system clock the next time it is recalculated.
Inserted comments in Microsoft Office PowerPoint PowerPoint does not have the full tracked changes functionality that exists in Word. Instead, PowerPoint stamps inserted comments with the current date. As with Word and Excel, new comments correctly reflect the updated system time. Previous time stamps are not changed retroactively.
E-mail items in Microsoft Office Outlook Every e-mail message is stamped with the time and date it was sent, based on the sender's system clock. Every message is also stamped with the time and date it was received, based on the receiver's system clock. For more detail about how meetings and appointments are affected in Outlook, see Microsoft Knowledge Base article 931667: Addressing daylight saving time using the Time Zone Data Update Tool for Microsoft Office Outlook. Time stamps are not retroactively updated to reflect changes in the system time on either the sender's or receiver's computer.
Tasks in Microsoft Office Project Tasks in Project are not linked dynamically to the system clock. The project schedule does not retroactively update to reflect changes in the system time.
Time functions in Project Functions such as NOW() and HOUR() use the system clock to determine the current time. When a change is made to the system clock, the function returns a value consistent with the updated date and time. When a change is made to the system clock, whether it is a change to the time zone or a change to or from daylight saving time, the function returns a value consistent with the updated system clock the next time it is recalculated. Time stamps are not retroactively updated to reflect changes in the system time.
Scheduler service reminders in Project The time when reminders are sent is based on the system clock. When a change is made to the system clock, whether it is a change to the time zone or a change to or from daylight saving time, reminders are sent based on the updated system clock.
Project creation date and check-out time stamps in Project Project creation and check-out times are based on the system clock. When a change is made to the system clock, whether it is a change to the time zone or a change to or from daylight saving time, creation and check-out time stamps reflect the time of the updated system clock. Time stamps are not retroactively updated.

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Frequently asked questions

Will documents created or modified in previous years during the extended-DST periods display the incorrect time property after the Windows operating system update for DST 2007 is applied?    

Yes, the times in the document's Properties will be off by one hour during extended-DST periods for 2006 and earlier, after the Windows operating system DST 2007 update has been applied. Previous extended-DST periods in the United States (prior to 2007) are those dates between the second Sunday in March and the first Sunday in April (for example, March 12, 2006, to April 2, 2006) as well as the week between the last Sunday in October and the first Sunday in November (for example, October 29, 2006, and November 5, 2006). Also, programs that display the time dynamically by referencing the system clock might also display these historical time stamps incorrectly — check with your software provider for more details.

  • To view the system clock in Category view, click Start, click Control Panel, click Date, Time, Language, and Regional Options, and then click Date and Time.
  • To view the system clock in Classic view, click Start, click Control Panel, and then click Date and Time.

Why are some time stamps and time references that are displayed in document properties affected by the DST shift?    

Programs that handle time stamps typically store those time stamps in Coordinated Universal Time (UTC). The advantage of UTC is that it is universal and invariant; it is not subject to local time zones or daylight saving time (DST). However, UTC does not display time in a format that is meaningful to most users, so computers convert UTC time to local time based on two factors: first, the time zone designated by the user, and second, whether DST is selected in the Date and Time item in Control Panel. The change in DST does not affect the historical time stamps as recorded in UTC, but the change might affect how time stamps are interpreted (and therefore displayed) by the Windows operating system and certain programs.

Should I apply the Windows time zone update?    

In general, computer systems should be updated to reflect the new DST rules. For most users, this means that you or your IT administrator should apply software updates to select Microsoft products, including various releases of Windows operating systems, servers, applications, and components.

Is there a fix available so that the date-modified time for the properties of documents that were created in previous extended-DST periods does not shift?    

Not currently. However, Microsoft is investigating the key requirements and development impact for this issue.

For more information, visit the Daylight Saving Time Help and Support Center.

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Applies to:
Excel 2007, PowerPoint 2007, Project 2007, Word 2007, Excel 2003, PowerPoint 2003, Project 2003, Word 2003