At a Victorian auction there is no cooling-off period. Sign the contract and the property is yours, defects included. Anything you want to know has to be known before you raise your hand, which means booking the inspection during the campaign rather than after.
In a private sale, residential buyers generally get three business days of cooling off. That is enough time to change your mind, but it is a very short window in which to organise an inspection, receive a report and read it properly. Inspecting before you sign is always the stronger position.
Between contract and settlement there is still value in a pre-settlement check, particularly on a new build or a property where the vendor agreed to complete repairs.