Well, sorry, but the sign is OK and completely legal. Parking signs like this, where parking and also loading is banned at certain times, then pay-for-parking is also at certain times, are commonplace.
So to convey the meaning of the Traffic Regulation Order for this location, several signs must be used together, with the most important one at the top. The top sign is a standard "No Waiting" sign with the times when it's not allowed. Underneath that is a sign saying when loading is not allowed, because is is an exemption to the sign above, unless signed separately as it is here. Then the final sign tells you when you have to pay for parking. Outside the hours on the three signs, parking is allowed and free. So Sunday has no restrictions at all as Sunday is not listed in any of the signs.
Please give us a GSV link to the exact location of parking so we can check out the sign and the road markings.
However, it does not look as if you have any credible appeal argument on the contravention itself, but appeals are often won on the council management of the enforcement process, so wait for others to comment.