I think you're making this overly complex.  

These rules...


    I'm paid every month;
    I'm paid always on the last possible day before the 28th day of the month;
    I'm paid always on a working day.


Come out to be "I'm paid monthly on the last week day."

That's an option on both Calendar and Microsoft Office.

[![enter image description here][1]][1]


  [1]: https://i.sstatic.net/yhWSh.png