When it comes to the science of bad decisions, few know as much as Dan Ariely. A professor of psychology and behavioral economics at Duke, Ariely (who also wrote the bestseller Predictably Irrational) has devoted his career to understanding why people make less than optimal choices. So when he says a time management misstep is both very common and very wasteful, you should probably sit up and pay attention.

Which is just what he did in the course of a completely fascinating Reddit AMA ('Ask Me Anything') recently. Amongst questions about what he wished he knew when he was younger and tips on how to avoid procrastination, Ariely also responded to one poster who wanted to know how he applies his research in everyday life. The answer is worth noting for everyone who is in the market for scientifically validated ideas to be more productive.

When are your two golden hours?

"One of the saddest mistakes in time management is the propensity of people to spend the two most productive hours of their day on things that don't require high cognitive capacity (like social media). If we could salvage those precious hours, most of us would be much more successful in accomplishing what we truly want," he responded.

Which raises another essential question--just when are those two golden hours? Apparently, it varies by the individual, but Ariely asserts that for most of us, mornings are a precious resource. "Generally people are most productive in the morning. The two hours after becoming fully awake are likely to be the best," he says.

Recent research covered here on Inc.com has shown that while Ariely is certainly right in asserting the importance of protecting your most productive hours, there is actually considerable variance in people's natural rhythms of wakefulness and concentration. Night owls (and other less often acknowledged patterns of sleepiness) really do exist. But that doesn't invalidate Ariely's key point.

His bottom line: "Your 'productive hours' are very important. Think about when those are, and then practice maniacal devotion to work during those hours."

Are you as vigilant as you should be in setting aside your best hours for deep, concentrated work?