Daylight Saving Time begins Sunday, March 10, delivering with the annual “spring forward” routine an extra hour of daylight in most places in America — most, because two U.S. states, Arizona and Hawaii, and a handful of territories don’t observe the twice-annual ritual of the changing of the clocks.

Officially, the time change takes place at 2 a.m. on Sunday, but most cellphones and digital devices automatically update to the adjusted time.

Although the beginning of Daylight Saving Time is often associated with the beginning of spring, the Spring Equinox isn’t until Wednesday, March 20.

Lawmakers in Hawaii and Arizona have declined to go along with the rest of the country on Daylight Saving Time. In Arizona, where the temperature can routinely reach a scorching 115 degrees, it’s a matter of retaining earlier sunsets and cooler evening temperatures. But the decision not to participate in the time adjustment isn’t absolute. Daylight Saving Time is observed on the Navajo Reservation in Arizona, which surrounds the Hopi Reservation, which doesn’t.

Because Hawaii is far south of mainland states with a latitude similar to Mexico City, lawmaker there haven’t seen the need to increase the hours of daylight. The U.S. territories of American Samoa, Guam, Northern Mariana Islands, Puerto Rico and the United States Virgin Islands also don’t observe Daylight Saving Time.

Here are five things to know about the time switch:

1. Daylight Saving Time not an American invention. Yes, Benjamin Franklin proposed the idea way back when and said Americans could conserve candles if they just got up an hour earlier. But the first known advocate of Daylight Saving Time was Englishman William Willett in 1905. His proposal to move clocks ahead by 80 minutes between April and October was rejected by the English Parliament, though, and the first country to implement the practice was Germany, which used it to save fuel during World War I..

The United States has used Daylight Saving Time off and on since 1918 as a wartime measure, but the current federal policy was first enacted in 1966 as the Uniform Time Act signed by President Lyndon B. Johnson. It has changed several times since then — notably in 1974, when Congress extended Daylight Saving Time to 10 months of the year following the 1973 oil embargo. But it was controversial, as many complained children were forced to go to school in the dark on winter mornings, endangering their lives.

Most of the changes have dealt with starting and ending dates. The Energy Policy Act of 2005 took effect in 2007 and called for clocks to “spring forward” on the second Sunday of March and “fall back” on the first Sunday in November. This year, that will be on Nov. 3.

2. Daylight Saving Time isn’t saving that much energy. The purported savings in the Energy Policy Act never materialized to a significant extent. A study by the U.S. Department of Energy in 2008 found the decrease in energy usage was hardly measurable — just 0.003 percent.

But a study from the University of California-Santa Barbara found the practice actually increased energy usage because an extra hour of daylight meant an extra hour of air-conditioner use. The authors of the 2008 study, which focused on the state of Indiana because it was slow to embrace the practice, said that based on conservative estimates, Indiana residents paid about $3.18 more a year for electricity. Statewide, that would add up to increased costs of $8.6 million a year.

3. Springing forward may be unhealthy. A study three years ago by the University of Michigan showed that the short-term risk of a heart attack goes up about 25 percent after the time switch. U-M cardiologist Dr. Hitinder Gurm, the study’s author, said that though it’s tough to pinpoint an exact reason, data showed a 25 percent surge in heart attacks on the first full work day after the time switch.

Another study published by Chronobiology International found that women who have had previous miscarriages who were undergoing in vitro fertilization were at much higher risk for miscarriages if their embryo transfers occurred during the 21 days following the start of DST compared to those whose transfers took place at other times of the year, including during the days after the switch back to Standard Time.

4. You’re less likely to get mugged and robbed when Daylight Saving Time is in effect. In a 2015 paper published by the Brookings Institute found that on the day DST begins in the spring, robbery rates fall by an average of 7 percent for the entire day. The decrease was much greater — 27 percent, during the evening hour that gained extra sunlight.

The reason: When DST isn’t in effect, the sunset and the end of the work day often coincide, and people are easier targets when they’re walking to their cars in the dark.

5. Fatigue and sleep deprivation associated with the time switch may increase “cyberloafing.” The number of Google searches for entertainment content, specifically “YouTube,” “videos,” “music” and “ESPN” rise sharply on the Monday following the time switch, according to a 2012 study published in the Journal of Applied Psychology.