@runninghorse observation times only exist to reduce the risk of PCNs being issued in error, they are not a defence. So for instance if a CEO issued a PCN with no observation time and you were walking back to the car with a visitor permit, the council would incur the cost in issuing the PCN and you would have the inconvenience of having to challenge it, but that's not the defence, the defence would be that you had gone to get a visitor permit and were returning with the permit without delay.
The same applied to loading and unloading, assisted boarding or alighting of passengers and so on.
However if the contravention did occur, the fact that the CEO didn't follow the observation time is irrelevant.
Looking at the council photos, the contravention does appear to be made out and the sign appears to be not far behind your car:






GSV:
https://maps.app.goo.gl/7Bispk4xs4BvuSwf6The traffic order is
The City of Westminster (Parking Places) (F Zone) (Consolidation No.1) Order 2011 and the relevant entry is item 147 on page 45, I can't see any obvious issues with the order but someone else might spot something.
In a case like this it would be best to get the background: why were you parked there, how long were you parked for, did you look for signs, and did you see any signs?
You obviously parked in a bay and while it is possible we might find a technical way out, it's much easier for us to help you if you can tell us whether there was an issue with the signage, whether you simply didn't look or whether you assumed that given the time of day it would be OK to park there.