CheekyChops has probably provided the correct link because most people who get a short term cash advance from Cash Converters take in non-jewellery items and use the 'Buy Back' scheme (which isn't the same as pawnbroking).
As CheekyChops indicates, you have only 28 days to buy items back under that scheme and you pay the same fee to get an item back whether you return one day later or 28 days later.
However, if you're taking jewellery into Cash Converters, you can use their 'true' pawnbroking scheme (which is regulated by the Consumer Credit Act). You then have 6 months to get your property back. During that period, monthly interest is charged, so you'll pay more if you return nearer the end of the 6 month period than at the beginning.
The link for the pawnbroking service is this one:
http://www.cashconverters.co.uk/services_detai l.php?s=pawnbroking
Chris