I parked on a single yellow line on a Sunday, believing the normal rule of: 'weekdays after 6:30pm (or other start time stated)and on Saturday and Sunday free and allowed to park' was applicable.
Please tell us where you got this idea of a "normal rule" from. The fact is there are no rules at all on when parking may be restricted, and in recent years, councils have been rolling out more and more parking restrictions and creating more and more Controlled Parking Zones (CPZs). Key to all this is the fact that all moneys received from parking penalties go straight into council coffers. So councils now employ literally
armies of CEOs (Civil Enforcement Officers), to patrol streets in big cities 24x7.
Are you a regular driver into Edinburgh ?
I had a look on the Edinburgh website and with the map facility, it shows you parked in "Controlled Zone 3" which is part of the Central Controlled Parking Zone. Typical of this dozy council the display doesn't tell you the controlled hour for the yellow lines ! However another search shows the yellow line restrictions as:-
Central Controlled Zone (CPZ)
Monday to Saturday: 8:30 am to 6:30 pm
Sunday: 12:30 pm to 6:30 pm
I suggest you submit representations that on your way into the street where you parked, you did not pass any sign telling you that you were entering a controlled zone and ask where the sign was that you missed that gave the single yellow line restrictions. Because most people just cough-up when they get a PCN, councils like Edinburgh get away with poor signage. Here is the sign at the boundary of the zone you entered, approaching from the south on the A701 : -
https://maps.app.goo.gl/3D8B9Rm4rd1B8geQ8
It tells you nothing about single yellow line times, and below it are two signs for a double0yellow line that applies 24x7 and needs no signs at all, in fact the signs contradict the legal meaning of double-yellow lines.Sorry, got the boundary wrong !!
Here are the signs as you drive up the A701
https://maps.app.goo.gl/jxuSE8nVuE6bhQ269And if f you drive up the Dalkeith Road, you also eventually get to these signs: -
https://maps.app.goo.gl/Afir7hRNxetMBnaw6These signs give the correct display and what the restricted hours are for the single-yellow lines. Double yellows need no times as they apply 24x7
Not knowing your route taken to get to where you parked, I cannot check for signs. but you must have passed one of these signs. If a sign is missing the PCN is void.