Gambling can be played in a variety of ways. You see, would it class as work if you are not paid in money? Does it class as a purchase if you decide to pay exchanging something? My take is that it is as long as you put there something that has value, from your own time, reputation and even intangibles... or works of art or anything. Time is money as they say.
^ Of course, even when you gamble for fun, there is still a risk involved.
You may lose money or other valuable things, such as your time or reputation if you are not careful. But gambling without money is a way to boost your knowledge of gambling. Just like what I did before, I gambled using an app poker game without using real money, my intention is to gain experience on how to play it. If you feel you gamble for experience and spend your time with that, then I disagree that not all them time you spend not jus because of money.