Fall Back This Weekend but Spring Ahead with Caution

The United States and parts of Canada are extending the period of Daylight Saving Time (DST) beginning in 2007.  Daylight Saving Time is a system of managing the changing amounts of daylight that occur during the year, with a goal of maximizing daylight hours during typical waking hours.  It was first proposed by Benjamin Franklin in 1784 but was not broadly adopted until the early twentieth century.  By adjusting clocks ahead by an hour, people can have more daylight available during the workday.  For example, in the case of someone who typically wakes up at 7 h, since in the spring the sun rises earlier each day, an individual would have to wake up at 6 h to take advantage of the daylight.  Instead, by moving the clock ahead by one hour, that person can continue to wake up at 7 h and enjoy more daylight.

Come next year, in accordance with the Energy Policy Act of 2005, Daylight Saving Time will start three weeks earlier than normal, with DST starting on the second Sunday in March and ending on the first Sunday in November.  In 2007, it will start on March 11 and end on November 4.  If you don't think that the upcoming changes to Daylight Saving Time are a big deal, change the time on your servers by an hour and see what happens.

Let's take a look at the ramifications. 

Perhaps the greatest impact will be for laptop and desktop computer users, most of whom who use the Windows operating system.  Microsoft will release a single global time zone update in November 2006 for Windows XP Service Pack 2 and Windows Server 2003 (and for Windows Server 2003 Service Pack 1).  This update will include updates for all DST-related changes from 2007 or which have taken place since the operating system's original release.  The updated time zone definitions will also ship with Windows Vista.  Windows XP SP1 and older operating systems will have passed their end of support dates and will not receive the update although they can be manually updated in some cases.

That covers operating systems but doesn't mean that we are out of the woods.  Software that supports calendar entries, such as Lotus Notes and Domino and Microsoft Outlook and Exchange, and other time-zone-aware calendar systems, are also impacted.  If you create an entry that falls within the extended Daylight Saving Time period before the application of extended DST rules, it will appear incorrectly after the extended DST rules are applied.  Entries that fall between March 11, 2007 and March 31, 2007 will appear an hour later than originally scheduled.  Entries that fall between October 28, 2007 and November 4, 2007 will appear an hour earlier than scheduled.  For example, if you create an entry today for 10 h on Monday, March 12, 2007, the entry will display at 11 h after the rules are applied.

What you can do to avoid problems:

First, avoid creating ANY calendar entries for the period March 11 -  March 31, 2007 and October 28 - November 4, 2007 until AFTER your operating system's Daylight Saving Time rules have been updated.  Some operating systems patches will only run after November 5, 2006 or the patch will activate only after November 5, 2006, even if applied earlier.  

Second, make certain to adjust or update your operating system to apply the changed Daylight Saving Times rules.

Third, remember that Daylight Saving Time is not observed in Hawaii, American Samoa, Guam, Puerto Rico, the Virgin Islands, and Arizona (with the exception of the Navajo Nation) and that the European Union version of Daylight Saving Time runs from the last Sunday in March through the last Sunday in October.