What port is considered for the 24-hour rule when cargo is trans-shipped from one foreign port to another before arriving in the U.S.? Per CBP regulation, the ISF is required to be filed 24 hours prior to the container being loaded on the vessel destined for the U.S. (the mother vessel), not the feeder vessel. CBP measures the timeliness of an ISF taking the Vessel Departure Date of the mother vessel destined for the U.S. – 24 hours to ensure the ISF transaction was submitted timely based on the date and time stamp of the ISF transmission. For trans-shipped cargo, CBP will consider the first port of departure for the mother vessel destined for the U.S.