Two years ago, when Congress passed a law to extend daylight saving time by a month, the move seemed a harmless step that would let the nation burn a little less fossil fuel and enjoy a bit more sunshine.

Representative Fred Upton, a Michigan Republican, predicted that children would rejoice at the prospect of an extra hour of daylight trick-or-treating on Halloween. But there is no rejoicing among corporate technology managers.

The change takes effect Sunday, as daylight saving time begins three weeks earlier (and ends a week later, on the first Sunday in November). And many companies are scrambling to reset BlackBerry e-mail devices, desktop PCs and big data-center computers used to automate payrolls, purchasing and manufacturing.

This puts the United States out of sync with the rest of the world for longer than usual this spring, almost certainly disrupting not only computers but also the business and travel schedules of companies, workers and travelers. Most of Europe goes to daylight saving time March 25, two weeks after America, while most of Asia, Africa and South America do not observe daylight saving time at all.