The simple answer is we don’t. We cannot prove the concept of time at all, but nothing makes sense without it do we fudge stuff to apply time to science.
At quantum levels time is even excluded as a variable in equations. There was even a chap called Rovelli who published articles about how time does not exist at all and its merely human perception.
However, from a practical perspective try and spend a week without acknowledging time as a thing and you’ll come unstuck pretty fast.