Skip to main content

Office Outlook Calendar

Impact of Daylight Saving Changes on Office Outlook Calendar Items

Updated 28th September 2007

Microsoft Outlook obtains daylight saving information from the host Windows operating system to determine the correct start time for future appointments. Consequently, it is important that Windows is updated to reflect any changes in daylight saving, including the introduction of daylight savings to a particular timezone for the first time.

However, when updates are applied, appointments which were created in the daylight saving period prior to application of the update will appear one hour later than originally scheduled. Consequently all-day events will span a 24 hour period across two consecutive days.

The following sections describe how Outlook users can re-adjust their calendars after application of a daylight saving update.


Important - The definition of the New Zealand time zone differs between Windows Vista and down-level Windows OSes. Specifically, the difference between OSes relates to which time zone rule each OS returns as the currently active rule; Vista returns the 2007 rule while other Windows OSes return the 2008 rule. Please click here for more information.

The New Zealand Daylight Savings Changes Guidance Document can be found here (XPS and PDF versions are available).

To find copies of the recent Daylight Savings presentations please click here.

The New Zealand daylight savings blog is constantly being updated with information as it comes to hand. Please ensure you are keeping your eyes on it.

Office Outlook 2000, 2002, 2003 & 2007 Calendar Update Tool

Use of the Time Zone Data Update Tool for Microsoft Office Outlook KB931667 is available to adjust calendar items after a Windows time zone update is applied. The tool may be used where Microsoft Office Outlook is used either standalone or in a Microsoft Exchange Server environment.

Exchange Calendar Update Tool

The Exchange Calendar Update Tool, described in KB941018 is recommended for enterprise environments to automate the adjustment of calendar items in a Microsoft Exchange Server environment.

Manual Adjustment of Appointments

For older versions of Microsoft Outlook or if tools are not available for automatic adjustment, appointments which fall between the old and new daylight saving transition times can be checked and adjusted manually. It is suggested that a hard copy of the calendar for the entire new daylight saving period is made prior to applying a Windows time zone update so that the original times for appointments can be checked.

A second alternative to using the Time Zone Data Update Tool is to export appointments in the daylight saving period to a .csv file before applying the Windows time zone update. Delete the appointments in the daylight saving period, then re-import them from the csv file. This causes the appointment times to be recalculated using the new time zone settings.