From Eternity to Here by Sean Carroll was one of the first books I read on time. It provided a good framework for thinking about time, introducing to me concepts such as the second law of thermodynamics of entropy. Entropy is a measure of disorder and within a closed system remains neutral or increases over time. An example of entropy is how an egg breaks when drops, you never see it reform itself.
Dr. Carroll also presented the Past Hypothesis, which argues the universe started in a lower entropy state than the present. This characteristic of time defines its asymmetric nature, or in other words, time only goes in one direction as far as we can tell. From this book the idea of an “Entropy Barrier” developed in the manuscript. This concept basically is the point past which life must either devolve or cease to exist. It created a clock for humanity, urgency in the story.