Parking Ticket - to pay or not to pay?

So I got a parking ticket at the weekend for not displaying a valid pay and display ticket in one of the Hebden Bridge car parks. Guilty as charged. It was at 08:50 in the morning and charges start at 08:00. I left the car in the car park overnight and used public transport to get home. In the morning I cycled to the car to pick it up but didn't get there until 08:50 just in time to watch the ticket being slapped on the windscreen. However, the reason I didn't buy a ticket is that the machine said you must have a ticket between 8am and 6pm. It costs 30p per hour. And I parked up at about 7pm. So should I have put 30p x 13 hours into the machine in order to be covered to 9am the next day.? Well I decided not to and risk it. But apparently, you can purchase pay and display tickets after 6pm and these commence at 8am the following morning when charging hours recommence. There is no signage to tell you this but if you stick 30p in the machine after hours then it will tell you this. So my conundrum is whether there are grounds for an appeal due to poor signage or should I just cough up (it's £50).