Not enough time in your day? Maybe because time itself is changing

I won’t pretend to understand all the physics in the concept, but this article I stumbled upon really fired my imagination.

Astronomers have known for years that the universe seems to be expanding at an increasing rate.  What was not known was why this acceleration was occuring:

Physicists assumed that a kind of anti-gravitational force must be driving the galaxies apart, and gave it the name “dark energy”.

However, to this day no-one has been able to say what dark energy is or where it comes from.

A Spanish professor, however, has come up with a fascinating alternative — perhaps time itself is slowing down.

If time has been slowing down, and clocks are now running more slowly than they did long ago, it would appear from our perspective as if things have been speeding up. Looking back over billions of years, galaxies would seem to be travelling away from each other faster and faster at various intervals since the Big Bang.

Somehow, this seems to make logical sense.  If we assume that time began with the Big Bang, it would seem that it should slow down and eventually stop.  Like pushing a toy car across the floor — it goes and slows and stops.

Why not?  Who says time has to be constant?