In late 2010, Contently co-founder Shane Snow worked every day from 8 a.m. to 2 a.m. on proving the viability of the company's nascent online publishing platform. But, as Snow found out, cramming more than a week's worth of work and meetings into an already jam-packed seven-day schedule is next to impossible, and exhaustion quickly set in. So, in 2011, "we made a 'no cowboys' rule and started forcing people to go home at 6 or 7 to get some sleep and live a little," he recalls. "It helped both morale and energy."

There's a whole library of books on productivity, like 168 Hours: You Have More Time Than You Think and The Time Trap, that proselytize the notion that you can and should get everything done. An admirable ambition--but one that exacts a toll. A study released in November by the Journal of Occupational Health Psychology, "Please Respond ASAP: Workplace Telepressure and Employee Recovery," laid out a definition for tele­pressure, or tele­stress: an urge to respond to work-related emails no matter when they're sent. An always-on work connection has very real health effects. The study found that employees citing telepressure suffered worse sleep, increased absences from work, and, as Snow discovered, higher levels of burnout.

All of this has given rise to a new school of time management, one concerned with zeroing in on your most important priorities, doing them well, and eliminating everything else--including keeping crazy hours. "The wrongheaded notion that you can manage time and that by managing it you'll get a ton of stuff done, cross everything off your to-do list, and live this super­human life really just sets people up for disappointment and failure," says Brigid Schulte, the author of Overwhelmed: Work, Love, and Play When No One Has the Time. "What you can manage are your priorities and your expectations of what you do in time."

Entrepreneurs have started taking cues from this new thinking, spurred by both hard-won experience and a slew of groundbreaking studies that identify how we work best. Recent research conducted by University of California- Irvine professor Gloria Mark found that it takes more than 23 minutes to get back on track after an interruption such as a meeting--and this has led LearnVest CEO and founder Alexa von Tobel to tweak her schedule. Today, her company's meetings rarely top 15 minutes. "I think of my calendar in 15-minute blocks, which helps keep meetings focused and on point," she says. She also never holds them on a Monday, because she feels that she's most productive on that day.

Azita Ardakani, CEO and co-founder of New York City-based communications agency Lovesocial, lets staffers tailor schedules to when they work best, noting that "the creative team usually gets juices flowing late at night and shouldn't be in at 9 a.m." Her employees are encouraged to not email colleagues and clients on nights and weekends. Such changes leave employees freer to let great ideas bake. "When you promote a space where employees can reflect on the unique nature of how they work best, and then put in general parameters and, most important, permission to foster that air to breathe and create, amazing things happen," she says.

Likewise, Vynamic, a health care management consultancy in Philadelphia, urges employees not to send emails on the weekends or between 10 p.m. and 6 a.m., a policy it calls zzzMail (as in: Catch some z's). Vynamic founder and CEO Dan Calista created zzzMail in 2012 after employees complained about stress in an annual engagement survey.

Such schedule-driven stress "is why meditation is suddenly in vogue in the work world," says Snow, who picked up the practice from his assistant while juggling deadlines for his book, Smartcuts: How Hackers, Innovators, and Icons Accelerate Success, and working on Contently. "It helps you be more calm and have a clearer mind to focus on the tasks that are more important." Which, by the way, are often far fewer than you think.

From the March 2015 issue of Inc. magazine