Plenty of well-worn time-management advice tells us how we should plan our day. Do the most important thing first. Never check email in the morning. Make a to-do list the night before. Don't schedule meetings right after lunch when everyone will be half-asleep.

But what if we organized tasks by when research shows it's actually most optimal to get them done? That's a question we started asking at On Leadership after coming across a recent study that shows the ideal time of day to make moral or ethical decisions is in the morning. And so, we pored over additional research (some academic, some perhaps less so) on tasks and timing. Below, a research-based weekday planner for what to do — and, perhaps more important, what not to do — at various hours of the day.

6 - 8 a.m. Send email. Many books may have been written advising us never to check email in the mornings. Time management experts say not to get mired in our inboxes first thing, or we won't get the critical things done. But of course, people do anyway, grabbing their phone off their bedside table, tapping away responses on their morning train, or giving themselves a breather once they sit down at their desks and drink their coffee.

Which is why sending email first thing might actually be the best time to do it. Research by marketing software company HubSpot shows that the highest click-through rate from marketing emails is on those sent around 6 a.m. or potentially a bit later, says Mike Volpe, HubSpot's chief marketing officer. He notes that it's ultimately best to know what time the person reading your email gets up and cleans out his inbox — so you can send your email after that, but before the day really gets underway.

8 a.m. Make decisions about ethical dilemmas. While the time here is somewhat arbitrary, recent research from professors at Harvard University and the University of Utah found what they called the "morning morality effect" in four experiments of undergraduates and working adults. In computer-based tests, participants were given the opportunity to cheat or lie in order to earn more money — and the experiments found that people were more likely to do both in the afternoon. "Self-control is like a muscle," says Harvard's Maryam Kouchaki, one of the co-authors of the study. "It's restored when we rest and eat. Basically, we have a limited amount of self-regulatory resources available to us at one time."

9 a.m. Avoid scheduling meetings. The hardest part about scheduling meetings isn't really finding the time when everyone involved will be bright-eyed rather than half-asleep. It's finding a time when everyone can actually attend. Keith Harris, chief technology officer of WhenIsGood.net, a bare-bones Web app for picking meeting times without sending a flurry of emails back and forth, dug into his software's data and examined 2 million responses to some 530,000 scheduled events. He found that first thing in the workday is when the fewest people say they're available. "Any time before ten, forget it," Harris wrote in an e-mail. "Your co-workers are still deep in their coffee and inbox." (Ahem. See above.)

1 - 2 p.m. Don't make cold calls (especially on Friday). One might think lunchtime would be a good opening for a new business lead, when you catch someone at their desk eating a sandwich and checking Facebook or ESPN.com. But research by James Oldroyd, a business school professor in Korea whom CBS Marketwatch called "the mad scientist of cold calling," finds that the worst time of day to make an unsolicited call is between 1 and 2 p.m. Far better is late afternoon (between 4 and 5 p.m.) or first thing in the morning (8 to 9 a.m.). That morning hour had 164 percent better results than the lunch hour in Oldroyd's analysis of more than a million cold calls. His findings also reportedly show that Thursday is the best day of the week, while Friday is the worst.

2:30 or 3 p.m. Schedule meetings (if it's Tuesday!). In addition to helping us find the worst time of day to try to get people around a table, WhenIsGood.net's Harris also scanned the data to find the best. The winner: Tuesday, at 2:30 p.m., is the day and time of the week when most people accept meeting requests. Harris ran the search for us earlier this week, and it confirmed similar results to when he first ran the numbers for a white paper five years ago and Tuesday at 3 p.m was the best. He speculates Tuesday afternoon stands out "because that is the furthest you can get from the deadlines at the end of the week, without bumping into the missed deadlines from the week before."

4 p.m. Do tasks that don't involve sending e-mail. HubSpot's Volpe says that if early morning is the best time to get people to act on an e-mail, late afternoon is the worst. The firm's analysis of millions of messages shows that 4 p.m. has the lowest click-through rate of any time of day, as people hurry to get out of the office and check things off before heading out the door. "Late in the day is bad," he says. "People’s brains are fried, and they're trying to clear things off in a cursory way."

4 - 6 p.m. Avoid sitting for an interview. If you catch wind the hiring manager has scheduled to interview several candidates over a single day or two — or you're applying for graduate school or some other program where such back-to-back arrangements are common — try not to be the last of the pack. In a 2013 paper by professors from the University of Pennsylvania's Wharton School and Harvard Business School, researchers looked at MBA applicants and found that when five similarly qualified candidates were interviewed on the same day, the last one to interview received lower scores than they actually should have. It's a phenomenon called "narrow bracketing," and it could apply to any situation when people have to make a large number of judgments over a short period of time. The researchers found a significant penalty, subconscious or not, to similarly qualified candidates late in the day. Might as well ask for the morning appointment if you can.

6 p.m. - late Do creative work, if you're a morning person. If it sounds counterintuitive, it is. Yet research actually shows that people do their best creative thinking when they're tired. The study, a 2011 paper from researchers at Albion College and Michigan State University, asked more than 400 students to solve six different problems at various hours over the course of the day.

They found that those who identified as feeling fresh and sharp in the morning did better solving problems late at night that required original thinking. For night owls, it was the inverse. Morning proved a better time for them to have bright ideas. Their explanation: Creative thinking requires us to approach problems from a different perspective, which is actually harder to do when we're clear-headed and can only see the obvious answer. If we need to concentrate, it's good for our brains to be "on." But if we need to think differently, it's easier when our brains are a little distracted and can short circuit the first answers that come to mind.

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