On the other coast, where it’s three hours earlier, nobody cares. Such is the glory of the Pacific time zone, which houses a smaller sliver of the country’s population—just 16 percent or so.

In the U.S. in the 1870s there were hundreds of time zones, because localities tended to run on mean solar time, i.e. noon was when the sun was highest in the sky.

Scott Yates, an entrepreneur and advocate for “ locking the clock,” says he’s agnostic about whether the U.S. lands on standard or daylight saving time—as long as it picks one.

In the 1800s, the three main sources of determining the time were the clock at the center of your town, the railroads, and the sun, but it would not be uncommon for all three to tell you different ...