In 1930, the influential economist John Maynard Keynes assessed how technological and economic advances had reduced the number of hours the average person worked. He predicted that within two generations, most people would work only three hours a day.

Working hard wouldn't be a problem. Filling all that free time would, for most people, be the problem.

While Keynes got a lot of things right, he swung and missed on that one. Technological advances have not freed up the average person's time. Neither have broader economic advances.

Nor has increased wealth. In fact, some studies show that the more money people make, the less time they think they have.

Add it all up, and money can't buy you happiness. 

Unless, purposefully and consciously, you use a little money to buy a little time.

In a 2017 study published in Proceedings of the National Academy of Sciences, researchers surveyed thousands of people who sometimes paid other people to perform tasks they didn't enjoy or didn't want to do. Like mowing the lawn. Or cleaning the house. Or running errands. Stuff they needed to do, but didn't particularly want to do.

Unsurprisingly, people who were willing to spend a little money to buy a little time were happier and felt greater overall life satisfaction than those who did not.

Correlation isn't always causation, though. Maybe the people who spend money to buy time are happier simply because they have the money to buy time? 

Nope. While relatively wealthy people who spent money to buy a little time were happier than relatively wealthy people who did not, people at the bottom end of the economic spectrum who spent money to buy a little time were happier than those at the bottom end of the economic spectrum who did not.

No matter how much you make, no matter how wealthy you are, buying a little time makes you happier. (With a couple of catches; more on that in a moment.)

Just to prove the causation point, the researchers conducted a further experiment. One week, participants were given $40 and told to spend it on any item or items they chose. The only restriction was that they had to use the money to buy "things." 

The next week, participants were given $40 and told they had to spend it on freeing up time. Cleaning. Maintenance. Delivery. Paying someone to do something they didn't want to do so they could use that time to do something they did want to do.

You've already guessed the result: When the participants bought time instead of things, they felt happier, less stressed, and more satisfied.

There is a catch. The researchers found that "spending too much money on time saving services could undermine perceptions of personal control by leading people to infer that they are unable to handle any daily tasks, potentially reducing well-being."

Granted, most of us can't afford to spend so much money buying time that we feel inadequate or incapable. But still: Making a conscious decision about which tasks to occasionally farm out is key. 

And why you decided to farm out that task. If someone always cuts your grass, then you've likely made that your new normal. You probably still feel too busy. You probably still feel time is scarce.

The key to buying time is to consciously decide how you will use the time your money freed up. Buying time will make you happier only if it feels intentional and purposeful--not because you don't have the time, but because you want to use the time you have differently.

Instead of cutting the grass, you might decide (again, to make this work you have to decide) to spend the time with family or friends. Or working on that side project you can't seem to get to. Or reading. Or working out.

In short, doing something you enjoy--doing something you want to do--with the time you bought.

That's when money can buy you a little happiness.

No matter how much you make.