The moment a payment can no longer be reversed — which is a legal question, not a technical one.
Settlement finality is the point at which a transfer becomes irrevocable and unconditional. Before it, a payment can in principle be unwound; after it, it cannot, even if a party subsequently fails.
It is a legal concept rather than a technical one, and jurisdictions legislate it specifically because insolvency law would otherwise allow completed payments to be reversed — which would make a payment system unusable.
The practical consequence is that 'the money has left' and 'the money cannot come back' are different moments, and the second is the one that matters when a counterparty is in difficulty.
Value date is when funds are usable. Finality is when the transfer can no longer be reversed, and the two need not coincide.
See also value date · settlement date · rtgs · clearing
We hold no settlement or clearing calendars. This entry defines the term and demonstrates nothing, because a near-miss borrowed from exchange closures would imply coverage that does not exist. See what we hold.