Two filings, two clocks
AMS is the carrier's obligation: the vessel operator (and NVOCCs, for their house bills) transmits the manifest — parties, cargo description, container details — and must have AMS acceptance before cargo can be loaded. The deadline is 24 hours before loading at the origin port. For an NVOCC, this means passing house B/L data to the carrier in time to make the master AMS transmission.
ISF is the importer's obligation: the ten importer-supplied elements (seller, buyer, importer of record, consignee, manufacturer, ship-to, country of origin, HS-6, stuffing location, consolidator) plus two carrier elements, due 24 hours before the vessel departs the last foreign port. The two deadlines are close but not identical — AMS is anchored to loading, ISF to departure — and both must be satisfied on a US ocean import.
Why the distinction matters operationally
Miss AMS and the cargo physically cannot load — the terminal won't accept it without manifest acceptance. Miss ISF and the cargo may sail, but the importer faces liquidated damages up to $10,000 per violation plus elevated exam and hold rates at destination. Because the two filings draw on overlapping but distinct data from different parties, coordination failures — an NVOCC late with house data for AMS, or a supplier slow to confirm ISF elements — are a common source of avoidable cost. Both are early-data problems: the information exists at booking, but must be marshalled days before traditional documentation would collect it.