When I make a debit card transaction, does the money leave my account straight away? When does the money reach the retailer?

A debit card transaction will usually be debited from your account on the following working day. However, if the amount of the transaction is above the floor limit of that retailer, the card issuer will earmark the funds on your account at the time the transaction is made. The time it takes for the money to reach the retailer is dependent upon the terms of the contract with their merchant qcquirer (bank).