On any commonsense view, this is a de minimis contravention, and they have served a money-grubbing PCN just to get money in. There can be no traffic management benefit in serving PCNs like this. Have the council put up a clock by the signs to ensure motorists know the correct time ? Of course not ! A car clock being slightly wrong is commonplace as we all know, and as the council know.
There is a successful appeal at London Tribunals where the adjudicator said what I have said; there must be application of commonsense. However, I don't have the case number, so hopefully somebody on here will post it up.
Of course if you submit reps to the council they will reject them, knowing that >95% of people then just cough-up, being unwilling to risk the full penalty at London Tribunals.
So the bottom line is that to hopefully get a result, you'll have to take them to London Tribunals and risk the full PCN penalty. Nothing to pay if you win, of course, and just the penalty if you lose, there are no other costs. However the council have to prepare an evidence pack and pay the adjudication fee, so may giveway just before the T hearing.