The Order of Time
The Order of Time by Carlo Rovelli is a lucid description of what time is and how it flows. It is based mostly on our best (and consensus) understanding of physics but also interlaced with some conjecture and his own work.
One of the main ideas is that time is not set as one moment, it depends on where you are (and how quickly it goes by depends on how far away we are from mass, e.g. the earth).
See for more a review by The Guardian.
One thing I really liked was how lucid he wrote, like David Deutsch with The Beginning of Infinity.