Clocks are set back at 2 AM because of Daylight Saving Time rules designed to shift an hour of daylight from evening to morning, aiming to better align waking hours with daylight and conserve energy. The specific 2:00 AM time is chosen to minimize disruption, since it is typically a period when fewer activities are occurring and it avoids changing the date on a Sunday in many places. Context and reasons

• Historical motivation: Daylight Saving Time (DST) originated to conserve energy and make better use of daylight, particularly during wartime and later for energy efficiency and daily scheduling.

• Operational rationale: The 2:00 AM moment is chosen because it’s late enough to reduce impact on daily routines and early enough to avoid changes during business hours, while also allowing the date change to occur smoothly in most jurisdictions.

• Practical effects: When the clock moves backward from 2:00 AM to 1:00 AM, people gain an extra hour of sleep or free time, but daylight hours shift earlier in the evening as DST ends, resulting in earlier sunset on subsequent days.

Regional differences

• Many regions that observe DST switch clocks in the early hours of a designated Sunday, with 2:00 AM being a common cutoff, though exact times can vary by country (some places use 3:00 AM or other local conventions).

• In the UK, the transition from BST to GMT typically occurs in the early hours of Sunday, effectively giving an extra hour of morning daylight as clocks go back by one hour.

Notes on the debate

• Some sources highlight health and sleep disruption concerns due to abrupt time changes, while others emphasize energy and scheduling benefits; opinions on continuing DST vary widely.

If you’re asking about a specific country or year, I can tailor the explanation to that jurisdiction and give the exact local time for this year’s change.