[kpil]

It depends. The banks nets the transactions a number of times during the day, normally using a central bank.

In the mean time the credit on your account is debited a 'float' account that accumulates any debt to other banks or third party payment system. Each fast payment system also typically have a reserved amount deposited as a guarantee in the event that a bank runs out of money.

It's a real cost to reserve money so there is a restriction on the sums.

Can the central banks speed up the settlement? Yes probably, but it's a lot of work to do.