since the switch press would only produce a trigger pulse at the port but not a constant low level.

yes 'continuous' for 20-40 milliseconds.

I doubt that a user that manages to press a switch for less than 20 ms actually ment to press it.

I have never had a complaint "the keys are too slow". If this was a qwerty keyboard for a very fast secretary, maybe, but this is a keypad.

I once had to increase debounce for human reasons because a keypad was located in a place where it was difficult not to 'brush' another key while moving finger to the desired one (200ms debounce to handle that).

Erik