OK, so here is the sign that you passed, and it has been there for four years as this GSV view is January 2021
https://maps.app.goo.gl/fXFbUajJaHKb3Ds26GSV for December 2020, shows an advance sign, although if it's still there, it should have been changed to reflect the vehicles allowed to pass that the current sign has on it.
https://maps.app.goo.gl/y73EiqLAHRnWo2aQ9So, did you jus misjudge the time, knowing the sign was there ? 5 minutes into the restriction times is rather too much for a de minimis appeal, frankly.
IN recent times, the councils have started to introduce web pages that accept representations against a PCN, and these have been found to be riddled with errors, such that appeals have been won on them. So see what the others say, but don't miss the PCN deadline to pay or submit reps