It has been said that tomorrow becomes yesterday because the earth spins. This is equivalent to the notion that the next atomic clock pulse becomes the last atomic clock pulse because of the decay of phase. In other words, it is a statement of the reversibility of quantum time.
While quantum time is reversible, gravity time's direction is set by the determinate paths of particles and so gravity time is not reversible. Gravity time is then completely predictable and determinate while the reversibility of quantum time means that quantum time is not determinate.
The way to explain time is with the parents and progeny of a causal set. Parents have children and from the family history of a causal set emerges what we call time. It takes more time for some progeny to emerge and that extra time is what we call distance in space. Quantum phase decay is then what sets time's arrow, both for quantum charge and quantum gravity and so entropy and temperature seem to have lost their way...
The notions of time and space are extremely useful for predictions of most action, but some predictions of action need the more fundamental notions of a causal set. A causal set orders actions by parentage and progeny and seems to be a more fundamental description of the universe.
However, quantum amplitude and phase superposition seem be an acausal superset whose norm becomes the causal set that we call reality. So it is wrong to say that the universe decays in time. Instead, the progeny of the universe result in fewer not more matter, but with greater force. From that family history emerges time and space...