Lee, the exchange rates do change every second and as Maxsteam wrote, there are no sites that can give you advice on where the FX rates will go in the furure. Sometimes on sites like fxcm.com you can look at predictions on various currency pairs by analysts - this doesn't cost anything but it is only a prediction and the professionals can get it wrong just as easy as me or you.
If you are taking a large amount of Rand for your honeymoon, you could consider buying some each month intil you go, or maybe using a currency broker to negotiate a better rate than the high street banks, but the better ones look for a minimum transaction size of £5,000 or £10,000 to do a deal.