Actually, the opposite is closer to right, although it's not that straightforward.

The way we usually imagine it is to halt any further technological developments or resource discoveries (i.e. take the world as it currently is), then allow market profit and loss processes to play out until the economy settles into a stable pattern of exchange (everyone's age stays fixed too).

You could also just imagine it as being that final state, where there are no remaining welfare improving changes to be made. Maybe that's what you meant by it being an instant.

It's either a hypothetical instant or the limit that market processes are approaching.