When must insurable interest exist in marine insurance?

Marine Transit Insurance covers the accidental damage or theft of goods transported by various mode including: sea, air, or by land. The coverage under this insurance policy typically includes loss of or damage to goods caused by fire, theft, sinking, or any natural disasters (Act of God perils). Coverage also extends to warehouses where the cargo is kept in the interim period, loading and unloading of cargo and can also include warehouse- to-warehouse. 
Marine transit insurance is essential for all businesses involved in shipment or movement of goods within a city, inter-city, or across countries. 
In marine insurance, there must be a physical object exposed to any perils and that the insured must have a valid legal relationship to the object ( cargo), and upon any loss or damage happening to the object, the insured will suffer a loss/liability. Hence the insurable interest in marine insurance should exist at the time of loss, although it may not have existed when the insurance was affected.  If the assured had no interest at the time of the loss, he cannot acquire interest.  Whereas in fire and accident insurance an insurable interest must exist both at inception of the contract and at the time of loss.