Those anticipating an extra hour of shuteye on Saturday night will have to hold out until next week.

The move back from daylight savings time to standard time takes effect at 2 a.m. on the first Sunday in November, rather than the last Sunday in October.

In 2005, U.S. legislators extended DST to 34 weeks in an effort to lower household energy consumption. Daylight savings time also started three weeks earlier this year. Advocates claim the changes will save up to 100,000 barrels of oil in the U.S. for every day of extra daylight.

Most Canadian provinces fell in line with the U.S. this year in an effort to harmonize, but the shift may have extended some some unforeseen consequences.

When the new daylight savings schedule began in March technology experts warned of a mini-Y2K glitch in personal computers, Blackberries, cellphones and MP3 players.

Health Canada also issued a warning that "springing ahead" could short personal medical devices, such as pacemakers and implanted defibrillators, and hospital information systems.

No major problems were reported.

Earlier this week, German researchers, reporting in the journal Current Biology, say the one-hour time adjustment of switching to daylight saving time can cause a significant disruption that has unintended effects on our bodies.

Just like other animals, the human internal clock -- called our circadian rhythm -- uses daylight to stay in synch with our environment as the seasons change, say the researchers.

Scientists concluded that when people are allowed to wake whenever they choose on their days off, their sleep timing follows the seasonal progression of dawn under standard time, but not under daylight saving time.

Researchers say this forced change on our circadian rhythms could have long-term effects on our health, but it is not yet clear what those effects might be.

The practice of adopting DST dates back to the First World War. DST was first implemented in Germany with the United Kingdom and other Allied countries following suit.

It was believed that DST would help to align traditional hours of work with daylight hours and would reduce the need for artificial lighting in place of employment.

The practice remains unpopular with farmers and other groups whose activities are set by the sun rather than by the clock.