There's lots of evidence that a huge percentage of most work days are wasted. One recent study found that almost half of employees could do their jobs in five hours or less. It's the latest of many similar studies.

Then there are the handful of companies (and whole towns in Sweden) that have cut their workweeks significantly with no fall in productivity. Or you could look at the psychology research that shows our brains simply don't have more than four good hours of work a day in them.

But if you accept the reality that most of us could probably get the same amount done in much less time, that raises an interesting question. How should we distribute these fewer, more concentrated hours? Should we work one day less? Start later? Take siestas?

Why you should leave work at 3 p.m. every day

On LinkedIn, star Wharton professor and best-selling author Adam Grant offered a thought-provoking answer to this question (hat tip to Quartz). In response to an Atlantic article detailing how the school day ends two hours before the end of the workday, creating a frantic scramble among parents to find childcare to fill those hours, Grant commented:

It's crazy that the school day ends two hours before the work day. But instead of making school days longer, let's make work days shorter: they should finish at 3 p.m. We can be as productive and creative in six focused hours as in eight unfocused hours.

This is an intriguing suggestion for a lot of reasons. First, parents will absolutely love it (particularly mothers, who studies show shoulder an unfair percentage of childcare duties).

But there's a second reason Grant's radical-sounding idea is actually a stroke of genius. As Daniel Pink outlines in his recent book When, the vast majority of us experience a dip in energy levels late in the day, right around the time Grant suggests we should all knock off work. In fact, research shows that we're effectively 20 percent stupider in the afternoon.

Most of us fight this "afternoon slump" with caffeine and white-knuckle determination, but despite our efforts, these hours are still far from our most productive. Cutting them from the work schedule, then, would give us the biggest bang in terms of improved quality of life at the cost of the least lost productivity.

Leaving early would also free up time for the sort of hobbies, reading, exercise, and social connection that a raft of studies show make us not only happier and more resilient but also more productive workers when we do hit our desks.

So what about it bosses, why not experiment and see what happens if you let your people leave the office at 3 p.m.?