When: The Scientific Secrets of Perfect Timing

by Daniel H. Pink

“[T]he performance change between the daily high point and the daily low point can be equivalent to the effect on performance of drinking the legal limit of alcohol,” according to Russell Foster, a neuroscientist and chronobiologist at the University of Oxford.15 Other research has shown that time-of-day effects can explain 20 percent of the variance in human performance on cognitive undertakings.

Alertness and energy levels, which climb in the morning and reach their apex around noon, tend to plummet during the afternoons.18 And with that drop comes a corresponding fall in our ability to remain focused and constrain our inhibitions. Our powers of analysis, like leaves on certain plants, close up.

Two American psychologists, Mareike Wieth and Rose Zacks, presented this and other insight problems to a group of people who said they did their best thinking in the morning. The researchers tested half the group between 8:30 a.m. and 9:30 a.m. and the other half between 4:30 p.m. and 5:30 p.m. These morning thinkers were more likely to figure out the coin problem . . . in the afternoon. “Participants who solved insight problems during their non-optimal time of day . . . were more successful than participants at their optimal time of day,” Wieth and Zacks found.21 What’s going on? The answer goes back to those sentries guarding our cognitive castle. For most of us, mornings are when those guards are on alert, ready to repel any invaders. Such vigilance—often called “inhibitory control”—helps our brains to solve analytic problems by keeping out distractions.22 But insight problems are different. They require less vigilance and fewer inhibitions. That “flash of illuminance” is more likely to occur when the guards are gone. At those looser moments, a few distractions can help us spot connections we might have missed when our filters were tighter. For analytic problems, lack of inhibitory control is a bug. For insight problems, it’s a feature. Some have called this phenomenon the “inspiration paradox”—the idea that “innovation and creativity are greatest when we are not at our best, at least with respect to our circadian rhythms.”23 And just as the studies of school performanc...

Human beings don’t all experience a day in precisely the same way. Each of us has a “chronotype”—a personal pattern of circadian rhythms that influences our physiology and psychology. The Edisons among us are late chronotypes. They wake long after sunrise, detest mornings, and don’t begin peaking until late afternoon or early evening. Others of us are early chronotypes. They rise easily and feel energized during the day but wear out by evening. Some of us are owls; others of us are larks.

What ultimately matters, then, is that type, task, and time align—what social scientists call “the synchrony effect.”

At the end of this chapter is the first of six Time Hacker’s Handbooks, which offer tactics, habits, and routines for applying the science of timing to your daily life. But the essence is straightforward. Figure out your type, understand your task, and then select the appropriate time. Is your own hidden daily pattern peak-trough-rebound? Or is it rebound-trough-peak? Then look for synchrony. If you have even modest control over your schedule, try to nudge your most important work, which usually requires vigilance and clear thinking, into the peak and push your second-most important work, or tasks that benefit from disinhibition, into the rebound period. Whatever you do, do not let mundane tasks creep into your peak period.

Lose weight: When we first wake up, having not eaten for at least eight hours, our blood sugar is low. Since we need blood sugar to fuel a run, morning exercise will use the fat stored in our tissues to supply the energy we need. (When we exercise after eating, we use the energy from the food we’ve just consumed.) In many cases, morning exercise may burn 20 percent more fat than later, post-food workouts.

Don’t drink coffee immediately after you wake up. The moment we awaken, our bodies begin producing cortisol, a stress hormone that kick-starts our groggy souls. But it turns out that caffeine interferes with the production of cortisol—so starting the day immediately with a cup of coffee barely boosts our wakefulness. Worse, early-morning coffee increases our tolerance for caffeine, which means we must gulp ever more to obtain its benefits. The better approach is to drink that first cup an hour or ninety minutes after waking up, once our cortisol production has peaked and the caffeine can do its magic.7 If you’re looking for an afternoon boost, head to the coffee shop between about 2 p.m. and 4 p.m., when cortisol levels dip again.

Afternoon circadian lows, the researchers concluded, impair physician vigilance and “affect human performance of complex tasks such as those required in anesthesia care.”

consider colonoscopies. I’ve reached the age where prudence calls for submitting to this procedure to detect the presence or possibility of colon cancer. But now that I’ve read the research, I would never accept an appointment that wasn’t before noon. For example, one oft-cited study of more than 1,000 colonoscopies found that endoscopists are less likely to detect polyps—small growths on the colon—as the day progresses. Every hour that passed resulted in a nearly 5 percent reduction in polyp detection. Some of the specific morning versus afternoon differences were stark. For instance, at 11 a.m., doctors found an average of more than 1.1 polyps in every exam. By 2 p.m., though, they were detecting barely half that number even though afternoon patients were no different from the morning ones.

Afternoons can also be deadly beyond the white walls of a hospital. In the United Kingdom, sleep-related vehicle accidents peak twice during every twenty-four-hour period. One is between 2 a.m. and 6 a.m., the middle of the night. The other is between 2 p.m. and 4 p.m., the middle of the afternoon. Researchers have found the same pattern of traffic accidents in the United States, Israel, Finland, France, and other countries.

These are the three principles of successful beginnings: Start right. Start again. Start together.

Many school districts—from Dobbs Ferry, New York, to Houston, Texas, to Melbourne, Australia—have heeded the evidence and shown impressive results. For example, one study examined three years of data on 9,000 students from eight high schools in Minnesota, Colorado, and Wyoming that had changed their schedules to begin school after 8:35 a.m. At these schools, attendance rose and tardiness declined. Students earned higher grades “in core subject areas of math, English, science and social studies” and improved their performance on state and national standardized tests. At one school, the number of car crashes for teen drivers fell by 70 percent after it pushed its start time from 7:35 a.m. to 8:55 a.m.6 Another study of 30,000 students across seven states found that two years after implementing a later start time high school graduation rates increased by more than 11 percent.7 One review of the start-time literature concludes that later start times correspond to “improved attendance, less tardiness . . . and better grades.”8 Equally important, students fare better not just in the classroom but also in many other domains of their lives. Considerable research finds that delaying school starting times improves motivation, boosts emotional well-being, reduces depression, and lessens impulsivity.