Millions of Americans in 48 states will set their clocks one hour ahead next weekend, launching nearly eight months of longer evening daylight during the spring and summer months.

The price? Losing an hour of sleep.

Here’s what to know as daylight saving time approaches at 2 a.m. on March 9.

A national war effort

The system for advancing clocks to shift daylight hours became official in the United States on March 19, 1918, when the Standard Time Act was signed into law, according to the U.S. Department of Defense. The law was intended to save energy costs during World War I.

About a year and a half after the war ended in 1918, the law was rescinded. Daylight saving time was again implemented during World War II, but dropped in 1945 when the war ended.

It wasn’t until the Uniform Time Act of 1966 that a consistent daylight saving time system was established twice a year, according to the U.S. Department of Transportation. It authorized state governments to exempt themselves from the system, independent of federal government permission.

A year-round system

Minnesota is among 20 states that have enacted legislation or passed resolutions in the last six years to implement year-round daylight saving time, according to the National Conference of State Legislatures. Federal law does not currently allow for a full-time system, meaning that Congress must approve the change prior to the states.

The U.S. Senate in 2022 passed the Sunshine Protection Act, which would effectively establish daylight saving time as the permanent standard time. However, no further action on the bill was taken.