The point is not to focus on time, or calculating how much of it you have; the point is to live in the present and step out of time. Forget it. The past is only in your mind. The future does not exist. The only real thing is right now.
If you are depressed you are living in the past. If you are anxious you are living in the future. If you are at peace you are living in the present. --Lao Tzu
The past isn't generally depressing and there are lots of things worth to be remembered. The past is not only in my mind, it is around me all the time and it is the context I'm living in.
The future needs some planning.
We just need to live in the present, but also have to make decisions based on past&present&future.
"'I want to feel alive!' Its easy. You cant think about the past. 'Why did I do that??' It'll just turn to anger. You also can't think about the future. 'Will it be okay?' It just turns to worry. In that case, hold on for dear life! Stake your entire life in here and now!"
It's worth a read, but perhaps it found me at the right time in my life.