<P> Clock shifts are usually scheduled at, or soon after, midnight and on a weekend to lessen disruption to weekday schedules . A one - hour shift is customary but twenty minute and two hour shifts have been used in the past . In all countries that use daylight saving, the clock is advanced in spring and set back in autumn; the spring change reduces the length of that day and the autumn change increases it . For a midnight shift in spring, a digital display of local time would appear to jump from 11: 59: 59.9 to 01: 00: 00.0 . </P> <P> The time at which clocks are to be shifted differs across jurisdictions . The European Union has a coordinated shift, shifting all zones at the same instant, at 01: 00 Coordinated Universal Time (UTC), which means that it changes at 02: 00 Central European Time (CET) or 03: 00 Eastern European Time (EET), the result is that the time differences across European time zone remain constant . North America shifts at 02: 00 but at the local time and is consequently uncoordinated so that, for example, Mountain Time is, for one hour, zero hours ahead of Pacific Time instead of one hour ahead in the autumn and two hours instead of one ahead of Pacific Time in the spring . </P> <P> The dates on which clocks are to be shifted also vary with location and year, consequently, the time differences between regions also vary throughout the year . For example, Central European Time is usually six hours behind North American Eastern Time, except for a few weeks in March and October / November, while the United Kingdom and mainland Chile could be five hours apart during the northern summer, three hours during the southern summer, and four hours a few weeks per year . Since 1996, European Summer Time has been observed from the last Sunday in March to the last Sunday in October; previously the rules were not uniform across the European Union . Starting in 2007, most of the United States and Canada observe DST from the second Sunday in March to the first Sunday in November, almost two - thirds of the year . Moreover, the beginning and ending dates are roughly reversed between the northern and southern hemispheres because spring and autumn are displaced six months . For example, mainland Chile observes DST from the second Saturday in October to the second Saturday in March, with transitions at 24: 00 local time . In some countries time is governed by regional jurisdictions within the country so that some jurisdictions shift and others do not; this is currently the case in Australia, Brazil, Canada, Mexico, and the United States . </P> <P> From year to year, the shift dates may change for political and social reasons . The 2007 U.S. change was part of the Energy Policy Act of 2005; previously, from 1987 through 2006, the start and end dates were the first Sunday in April and the last Sunday in October, and Congress retains the right to go back to the previous dates now that an energy - consumption study has been done . Proponents for permanently retaining November as the month for ending DST point to Halloween as a reason to delay the change--to provide extra daylight on October 31 . In the past, Australian state jurisdictions not only changed at different local times but sometimes on different dates; for example, in 2008 most DST - observing states shifted clocks forward on October 5 but Western Australia shifted on October 26 . </P>

When does day light savings start and end