Time is a construct that we as humans spend a lot of effort in defining, using, cursing & vilifying, and expending. As we define it, time is a human "invention". In physics, time is a fundamental quantity - a variable to be plugged into an equation or to affect another physical measurement. In quantum physics, time as we know and measure it has been shown not to exist. (see "double slit experiment", if you care to study this - then there is the interpolation of that experiment on light over deep-space distances - but I digress) This post is going to be confined to our traditional understanding and definition of time.
I read something years ago about time that was one of those things that stuck with me and affected my thinking ever since. It went something like this:
Time is the ONLY thing that is totally equal for everyone. Rich or poor, tall or short, happy or sad; we all have the same amount of time - 24 hours a day, 60 minutes an hour, 60 seconds a minute. (I do know we don't have equal lifetimes, but every hour is the same for all) Time is the great equalizer. We humans spend a lot of "time" explaining why we don't have "time" to do this or that. But, we all have the same time each day. What we really mean is: "I do not chose to use my time for that", or "I had too many other things that took priority over that thing for me to do it".
Time can be reviewed, remembered, relived, reviled; but it cannot ever be renewed or reused.
Once time is expended, it is gone. So besides being a great equalizer, time is one of the factors that define our life that once used cannot be renewed or replaced. Time passes and is gone. Time has been compared to a river, constantly flowing away from us. (That is not quite correct as the hydrological cycle keeps all the same water in use in perpetuity - but I digress again!)
Use your time wisely.