Does the fact that the contravention is for something they prohibit, rather than not paying for parking have any relevance to the argument on time stamp?
That would be a different argument, and whether it had any legs would depend on what the signage at the site says. If no parking is offered at all at the site, e.g the Minster signs just say "No Parking Allowed" or similar, then there is an argument that as the signage does not offer parking on certain terms, then no contract can be formed, as no offer is made. If however the signage offers parking on certain terms, and one of those terms is that you agree to only park within marked bays, or agree not to park on yellow lines, that argument would not succeed.
