I was talking with Richard Branson about his new class on MasterClass and asked how he decides where to spend his time. (Clearly he's a busy guy; the Virgin Group serves as the corporate umbrella for 40-plus travel, hospitality, financial service, media, and space companies.) 

I also asked for advice for aspiring entrepreneurs who have an idea for a business, but can't find the time to actually start it. 

I assumed Branson would discuss things like schedule optimization. Prioritization. Organization. The usual suspects.

Nope: 

Time is interesting. I devote three or four hours a day to finding fun things to do to keep really fit. Tennis. Biking, Kite surfing. The gym. People will say, "How can you find so much time for your body?"

If you find the time for your body, and you're feeling really great ... it's funny: Your day just expands by another three or four hours, and you're so much more productive.

Granted, there's a chicken-versus-egg aspect involved. If you're extremely busy, carving out even an hour to get fit can seem impossible. It's hard to expand your day through feeling great if you don't have the time to do things to help you feel great.

But that's where the second part of Branson's answer comes in. 

Some people are very entrepreneurial, but not necessarily great at running businesses. Or don't have the time to try. Find people to help you put your idea into practice, and continue in your profession until you see whether your idea has traction. 

And if it does gain traction, it's funny: Your day just expands. We tend to pursue things that are exciting, that are fulfilling, that we're successful at doing ... one day you'll realize, almost like magic, that you found more time to work on your startup than you ever imagined possible.

That's the real secret to time management.

Most time management advice involves some degree of willpower. Sticking to a schedule. Checking off to-do lists. Doing what you need to do next, and next, and next -- not what you want to do.

But willpower is finite.

That's why Branson finds fun ways to keep fit. For him, deciding to spend an hour on a treadmill is a tough choice; deciding to spend an hour playing tennis with friends is effortless. In my case, deciding to grind away for an hour on an exercise bike is a fairly tough choice; deciding to ride outdoors is nearly effortless.

We both gain energy, and productive time, from feeling better -- without having to force ourselves to exercise. Finding the time is easy, because it's fulfilling. Beneficial.

And fun.

Now extend that premise to starting a business. Running your own business means making hundreds of decisions, and unfortunately we all have a finite amount of mental energy. Granted, exercise can improve memory and cognitive skills. Exercise can lower symptoms of fatigue by as much as 65 percent. Exercise can help you better manage stress. (That's another reason Branson devotes time to finding fun ways to keep fit.)

Even so: Eventually, your willpower starts to fade. Decision fatigue starts to creep in. 

And time starts to disappear.

If you want to start a business, start from a basis of fun. No matter how great the idea, no matter how great the opportunity, if you won't enjoy the work, you won't find the time.

Then consider fulfillment. If success, no matter how great, won't make you feel better about yourself, if you won't feel a sense of accomplishment and actualization, you won't find the time.

No matter how hard it might seem, carve out a little time to get started. Find people to help you see if your start idea has merit. (Make sure they're people you'll enjoy being around; if you don't, you won't find the time to work with them.)  

If your idea does gain traction -- if you sell a few products, land a few clients, start to build a community, etc. -- almost magically, your day will expand. Your time will expand. 

Without thinking about it -- or even realizing it happened -- you'll find more time.

Because we all tend to pursue things that are exciting, fulfilling, successful -- and fun.