* Make month and weekday names lowercase
* Replace AM and PM with Polish words
* Adhere to recommendations wrt short weekday names
https://sjp.pwn.pl/poradnia/haslo/dni-tygodnia-i-inne-roznosci;1788.html
* Fix a typo
* Inflect month names
I assume they're always used as part of the full date,
and in this case months are always inflected in Polish.
* Use roman numerals in place of short month names
I could not find any actual use of short month names in Polish.
The only mentions are from people trying to translate English
conventions into Polish - typically in software.
In https://sjp.pwn.pl/poradnia/haslo/dni-tygodnia-i-inne-roznosci;1788.html
Mr. Bańko answered (translation mine):
Abbreviations of month names are less common, numbers are used instead.
Such abbreviations can be created [...]. However, one must take into account
that the reader will not understand them.
I decided to go with a convention that's in actual use, rather than to
force an English convention which is alien to non-software dev Poles.