Post History

I dont think anyone can make a universal calendar because time flows more slowly or more fast between different regions in the universe or it can even go backwards if you come close to a rotating black hole.

And a planck unit of time is not the smallest amount of time ,the planck time is defined as the planck length/c and the planck length is a scale at which quantum gravitational effects become important. 

So again since the rate of flow of time isnt universal we create a calendar based on the measurement of the clock of 1 second at the surface of Earth.