<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html lang="en-us" xml:lang="en-us"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <meta name="security" content="public" /> <meta name="Robots" content="index,follow" /> <meta http-equiv="PICS-Label" content='(PICS-1.1 "http://www.icra.org/ratingsv02.html" l gen true r (cz 1 lz 1 nz 1 oz 1 vz 1) "http://www.rsac.org/ratingsv01.html" l gen true r (n 0 s 0 v 0 l 0) "http://www.classify.org/safesurf/" l gen true r (SS~~000 1))' /> <meta name="DC.Type" content="concept" /> <meta name="DC.Title" content="Daylight saving time" /> <meta name="abstract" content="Use this information to understand daylight saving time (DST). Find out what DST is and which time zones use DST." /> <meta name="description" content="Use this information to understand daylight saving time (DST). Find out what DST is and which time zones use DST." /> <meta name="DC.Relation" scheme="URI" content="rzaticoncepts.htm" /> <meta name="DC.Relation" scheme="URI" content="rzatitime.htm" /> <meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" /> <meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1998, 2006" /> <meta name="DC.Format" content="XHTML" /> <meta name="DC.Identifier" content="rzatidst" /> <meta name="DC.Language" content="en-us" /> <!-- All rights reserved. Licensed Materials Property of IBM --> <!-- US Government Users Restricted Rights --> <!-- Use, duplication or disclosure restricted by --> <!-- GSA ADP Schedule Contract with IBM Corp. --> <link rel="stylesheet" type="text/css" href="./ibmdita.css" /> <link rel="stylesheet" type="text/css" href="./ic.css" /> <title>Daylight saving time</title> </head> <body id="rzatidst"><a name="rzatidst"><!-- --></a> <!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script> <h1 class="topictitle1">Daylight saving time</h1> <div><p>Use this information to understand daylight saving time (DST). Find out what DST is and which time zones use DST.</p> <p>Many countries or regions specify that their local system time be adjusted forward or backward by one hour, to accommodate annual changes in the number of daylight hours. This change might also be accompanied by a change in the time zone name. For example, in Toronto, Canada, 1 p.m. is announced in the winter as 1 p.m., Eastern Standard Time (EST), and is announced in the summer as 1 p.m., Eastern Daylight Time (EDT). Daylight saving time is also known as <dfn class="term">Advanced Time</dfn>, <dfn class="term">Summer Time</dfn>, or <dfn class="term">Legal Time</dfn> (with Standard Time also known as <dfn class="term">Winter Time</dfn>) in certain countries or regions. Daylight saving time adjustments in the southern hemisphere are opposite to those in the northern hemisphere.</p> <p>A general rule for DST changes is that the change from Standard Time to DST needs to be completed before 03:00 (local time) on the date or day that DST is to begin. Likewise, when changing from DST to Standard Time the time change occurs between midnight and 03:00 (local time) on the date or day when DST ends.</p> <p>Also note that if you use other automatic methods to adjust for DST in combination with a time zone that observes DST, you need to disable the other methods. Otherwise, your local system time might adjust more than 1 hour for DST.</p> </div> <div> <div class="familylinks"> <div class="parentlink"><strong>Parent topic:</strong> <a href="rzaticoncepts.htm" title="Use this information to understand time management concepts such as time zones, coordinated universal time (UTC), and daylight saving time (DST).">Concepts</a></div> </div> <div class="relconcepts"><strong>Related concepts</strong><br /> <div><a href="rzatitime.htm" title="Use this information to understand time concepts such as time zones, coordinated universal time, system time, and job time.">Time</a></div> </div> </div> </body> </html>