Time is a weird subject. Almost everything in Physics becomes weird when you take it far enough. Maybe that's why I enjoy it? You wake up a sunny morning well pleased with your world, then you open a physics book, debate, whatever

and nothing is the same any more.

Let's see what we know of time. It has a direction for us, here and now, I will die some day.. If you don't agree to this one you're in trouble.. It might be a symmetry, or as Penrose suggested, an asymmetry, or just one way, meaning that it either communicates/commute in different 'directions', equally well or unequally, or that it doesn't communicate/commute at all. All of those questions are mathematical, coming from Einstein's field equations as I understands it, not experimental.

We have some very weird stuff, that I'm hung up on, existing. Entanglements, Tunneling's, Although personally I think Entanglement is the weirdest idea I know. But it's there, for real, no joke.

But time has a direction, so how do we measure that direction? It doesn't have any tags on it telling us when one 'swamba dimba' is gone, does it? We have to find our own ways of sorting it into 'quantities'. And physics is weird.

In physics you have Planck time, and Planck size and they are related to a ' smallest propagation of 'c' ' But why?

"The Planck time is the unique combination of the gravitational constant G, the relativity constant c, and the quantum constant h, to produce a constant with units of time. For processes that occur in a time t less than one Planck time, the dimensionless quantity tP / t is greater than one. Dimensional analysis suggests that the effects of both quantum mechanics and gravity will be important under these circumstances, requiring a theory of quantum gravity. All scientific experiments and human experiences happen over billions of billions of billions of Planck times, making any events happening at the Planck scale hard to detect."

And

In 1898, Max Planck discovered that action is quantized, and published the result in a paper presented to the Prussian Academy of Sciences in May 1899.[19][20] At the end of the paper, Planck introduced, as a consequence of his discovery, the base units later named in his honor. The Planck units are based on the quantum of action, now usually known as Planck's constant. Planck called the constant b in his paper, though h is now common. Planck underlined the universality of the new unit system, writing:

...ihre Bedeutung für alle Zeiten und für alle, auch außerirdische und außermenschliche Kulturen notwendig behalten und welche daher als »natürliche Maßeinheiten« bezeichnet werden können... ...These necessarily retain their meaning for all times and for all civilizations, even extraterrestrial and non-human ones, and can therefore be designated as "natural units"...

Planck's paper also gave numerical values for the base units that were close to modern values."

And it's to me a 'constant'. Constants are the closed doors you meet in Physics. There might be a key to open each one, but then you'll have to find a new way to walk up to it. They do not apologise, and they do not care that 'common sense' demands a answer for why they are there. They just are the 'rules of the game'.

So? We have 'two' constants here 'c' and the Plank units. And times measurement is a function of your choice of 'clock' measuring them. It's quite natural to combine them. The problem is that Relativity discuss a lot of other definitions for how time comes to be, relative the observer, and that catch peoples interest. Especially those of you mathematically inclined. And the idea of a time symmetry makes people forget what they actually see, that we all die.