20th Century Banking Timeframes

Discovery's debit order from my FNB account takes 6 days to clear into my credit card. This is the second time now and their call centre just says it's the way it is. This is a ridiculous amount of time given it's all digital. How can Discovery just say that a transaction can hold your money for 20% of a month!?!? Especially during such tough economic times! "Up to 4 working days" is not good enough... Discovery cannot be archaic like that. I'd understand 24-48 hours, even that I find absurd though as we live in a digital age.