Tell HN: Today is the 21st day of the 21st year of the 21st century

This is all ultimately arbitrary

Almost. it’s the 21st day of the 22nd year... 2000 was year 1.

Today 9 PM will be 21st hour of the 21st day of the 21st year of the 21st century.

You could say the same thing in every month of this year.

I hope you wrote it at 21:21:21 ;)