One of the things that intrigued me most in the book The Power of Now by Eckhart Tolle is that the only time that really exists is present, that the concept of time is a man-made concept and there is no such thing as tomorrow or yesterday. The way he explains is really thought provoking and convincing. I was sold. But recently, I started thinking more about this and I have found that I actually disagree with that.
I don't think time is a man-made concept. It's as natural as life itself. The main reason for this is that our lives are finite, that we will all have a last day on Earth. And each day that passes brings us closer to our last day. Let's suppose my last day is 60 years away from today. Then 50 years from now, my last day will be only 10 years away. Which means today and 50 years from today will be two very different days for me, especially since our physical health, mental health, and preferences change very systematically as we age. Then it follows that tomorrow is different from today (albeit less dramatically), and today is different from yesterday. Each day is different. And the reason each day is different is that each brings us one day closer to our last day. And that's the key idea behind the concept of time.
In the afterlife, if you believe in it, we will live forever. There, we would have no concept of time, because life would be infinite. Our last day would be infinity days away from today, and infinity days away from 50 years from today. Because of this, today would be no different from 50 years from today. Likewise, everyday will be exactly the same as today. There will be no tomorrow or yesterday. Because of this, there would be no such thing as time. We would simply not have any such concept.
Interestingly, this understanding helped me get rid of my apeirophobia (the fear of eternity -- yes it's a thing). Because without time, the idea of boredom cannot exist. Nor can impatience or haste. This one thing -- having an everlasting life -- would destroy the entire concept of time itself. And with it, it would also destroy everything else that depends on the concept of time (including apeirophobia).