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Introduction

The year 2007 brings with it a change in Daylight Saving Time (DST) rules. A provision of the Energy Policy Act of 2005 changed DST to begin three weeks earlier and end one week later, effective in 2007. Starting this year, DST will begin the second week of March and end the first week in November (March 11 and November 4 in 2007). This is the first modification to the DST rules in the United States in 20 years. Other areas that follow US DST rules, including Canada and Bermuda but not Mexico, are similarly affected.

The time of day that we begin and end observing Daylight Saving Time has not changed; in the United States DST still begins at 2:00 am standard time in the spring, when clocks are set forward to 3:00 am, and ends at 2:00 am daylight saving time in the fall, when clocks are set back to 1:00 am.

This document outlines the impact of the DST change on computer systems and devices. The goal is to raise awareness for users and in particular system administrators so they understand the potential impact of the DST changes and can take request or take action to avoid problems related to the change. There are two major recommendations:

  • Apply system patches to implement the new DST starting and ending dates

  • Consider whether corrections are needed to systems that store date/time values, such as calendar software or spreadsheets

The sections below go into more detail on each issue. A companion document contains a collection of links to vendor web pages where DST updates are discussed and patches are offered.

The change in DST rules will remind some of the Year 2000 (Y2K) problems in programs that referred to a year using two digits. The impact of the DST changes should be significantly smaller but is still a concern for those involved in preparing for the change. Many systems will be corrected simply by applying automatic updates from the system vendor in advance of the March 11th deadline. The result of having out of date rules is also smaller, with systems being off by an hour instead of a hundred years (or failing completely). On the other hand, there may be significant impact on computer support organizations, especially in cases where meetings in a calendar system need to be corrected manually.