What is your Epoch?

While developing an application to handle Microsoft Excel files, I had a trouble in converting timestamp columns to practical values (i.e., dates in my applications).
I then searched for a solution in the source code of a module Iā€™m using, SimpleXLS, and the comment on that line puzzled me:
Dates in Excel are stored as number of seconds from an epoch.  On
Windows, the epoch is 30/12/1899 and on Mac it's 01/01/1904

Is the epoch something different from what I was used to think about? And to be honest, being grown as a Unix devotee, I thought it was a time(2) clearly states:
% man 2 time
       time() returns the time as the number of seconds since 
       the Epoch, 1970-01-01 00:00:00 +0000 (UTC).

So, according to Unix, and POSIX, Epoch is set at 1970-01-01, while according to proprietary software it is not. Somehow this does not suprise me at all!

Therefore I searched a little more, and according to this Wikipedia Page on Epoch it seems there are a lot of different epochs around the world.

I think this is the human nature: we cannot agree on religions, why should we agree on times?

The article What is your Epoch? has been posted by Luca Ferrari on November 19, 2019