In practice: the detention clock usually starts when the full container leaves the terminal and stops when the empty is returned to the depot the carrier names. Slow unloading at the warehouse, long inland trucking or border crossings, and returning the empty to the wrong depot all add days. Some carriers give one combined free-time allowance for demurrage and detention, others count them separately, so check which applies.

Example: a container is trucked from Mombasa to Nairobi, unloaded and returned in 16 days. With 10 days of detention free time, 6 days are charged. Recording the gate-out and empty-return dates in the case file makes the bill easy to check.