It’s fast: When you pay a cheque from another bank into your bank, the bank will often hold that money for several days, because it can’t trust that the funds are really available. Similarly, international wire transfers can take a relatively long time. Bitcoin transactions, however, are generally far faster.
Transactions can be instantaneous if they are “zero-confirmation” transactions, meaning that the merchant takes on the risk of accepting a transaction that hasn’t yet been confirmed by the bitcoin blockchain. Or, they can take around 10 minutes if a merchant requires the transaction to be confirmed. That is far faster than any inter-bank transfer.