Nedbank payment to Nedbank takes 3 days. Nedbank to Capitec immediately. Why?

Just a question...

How is it that Nedbank debit my bank account with a debi check (or debit order) for my Nedbank credit card payment, and it takes up to 3 or 4 days to show, (or "clear"), while Capitec takes a debit order from my Nedbank bank account for my Capitec credit card payment on the same day, and it immediately reflects in my Capitec account?

I really don't understand this. Maybe you can clearly explain this to me?