You could go with the simple(no disrespect intended) argument suggested.
Maybe for later..
The single pavement parking sign is 24/7;
It conveys the meaning that vehicles MAY park (not must, may) on the footway within marked bays;
The so-called marked bays are actually parking places and are in force in accordance with their respective traffic signs;
So, what would happen if a motorist parked on the carriageway during the time the parking places are restricted? If they are 'marked bays' in the context of footway parking, then nothing is permitted, it's optional. But I bet you'd get a PCN for not parking wholly in a bay!
In short:
You parked on the footway because you assumed that as the footway parking sign applies 24/7 and the marked bays only Mon-Sat **** then, as the time was outside this period, the markings didn't apply. If the council think that the markings apply 24/7, then why have they placed signs to the contrary within these areas?
They are totally confused; the pavement parking sign is incorrect and should be removed; the signs in the parking places should be replaced with item 3 Part 4 here:
https://www.legislation.gov.uk/uksi/2016/362/schedule/4/made