When I paid mine this morning, it said that it could take up to 2 days to process on the credit card. I'm not sure if that answers your question, though...?
I think the OP is asking about the timing since he is in England and if he uses a credit card, the credit cards do the currency exchange. So if the pound is worth more (relative to the dollar) right now, he could come out ahead by paying now rather than wait until later..
Paul - If you haven't already, try asking your question on the UK DVC Discussion board. Someone there may have experience with credit cards used internationally. I pay my dues with a credit card and expect it to be charged immediately. However, I have no idea how the credit card companies decide what day to calculate exchange rates for those who are not using U S dollars to pay.