I got caught on the same one Jane, lost track of time and thought I was within the allowed parking times, and popped in the post office.
I actually joked with TfL on Twitter at the time for catching me so swiftly. Like yourself, I knew I was in the wrong, so paid up.

That said, I got a ticket in Bromley over turned after a year fighting with them, for poor signage etc.

Totally agree, the timings for some of these things don't seem to fit the road. But like bus lanes, there are a few groupings of timing to make things a little more standard. Not sure which is better, different times for each location, or simplicity of knowing it will be one of a few timings.