“When you enter the bedroom, it should be a sign for your body that it’s time to go to bed,” Dr. Basner said.

That’s why he found the results of his analysis so encouraging: The public, it seems, is developing a healthier relationship with sleep.

Americans were able to eke out extra sleep largely by heading to bed sooner and, to a lesser degree, by waking up later, the researchers found.

That changing weeknight bedtime — a shift earlier of 66 seconds each year — was made possible in part by less reading and television watching before bed.

While Americans added about 30 seconds of television watching to their weekday routine each year, they were doing less of it in the hours before bed, freeing themselves to go to sleep a bit earlier, the researchers found. Each year, the number of people who said they watched television or movies before bed on weeknights shrank by about 0.22 percent.

That finding aligns with data from Nielsen, the television research firm, which suggests that Americans are taking more control over how they view shows and movies by watching less live television late at night and more through other means, such as internet-connected devices.