Every D&D dispute reduces to the same question: on which days was this container somewhere it should not have been, and whose fault was that? The carrier's invoice answers with one set of dates. The terminal, the trucker and customs each have their own. The desk's job is to put them on one line.
The events that matter
Discharge (when free time usually starts). Availability (sometimes when it starts instead). Holds — customs, terminal yard, carrier — which may be excluded. Gate-out full (demurrage ends, detention may start). Handover to the trucker (the responsibility boundary). Empty return gate-in (detention ends). And the invoice date, which matters for time-bars.
Each of these lives in a different document from a different party, and each party's timestamp serves that party's interest.
Sources disagree
The invoice says gate-out on the 9th; the EIR says the 8th at 16:40. The depot says empty returned on the 15th; the trucker's EIR says the 12th. Each disagreement is a day of money. The timeline does not resolve these by picking one; it shows both with their sources and applies the contract's source-of-record clause if there is one. The desk decides what to argue. The honesty is the strength: a letter that says "your invoice shows the 9th; the attached EIR, countersigned at your gate, shows the 8th" is hard to reject.
Exclusions
A customs hold from the 4th to the 9th is five days the contract may exclude from free time. On the timeline it is a shaded band with the customs notice attached. The recomputation shows the free-time clock paused. Without the timeline, the clerk is arguing from memory about dates that happened six weeks ago.
When the timeline says don't
Sometimes the events line up exactly with the invoice, and the only argument is that the charge is unfair. The file says so: contractual basis weak, goodwill request drafted, send at your discretion. Desks that send only strong disputes get paid faster on all of them.