No good "quickly looking at the sign" in London, or you'll get a lot more PCNs ! You were 48 minutes too early to park there.
There may, however, be a "technical" challenge available, so hopefully the expert on these will soon be along. Technical appeals are for when the council, (or TfL also), do not follow the process and the regulations that they MUST do in order to legally enforce PCNs. At the moment, the PCN looks OK to me.