The time it takes for something to happen is very much a matter of perception and sensitivity.
We like to give names to things that happen. The French Revolution. When did the revolution actually happen? It depends on what you choose as the defining moment. If there is a sequence of events that led to it, it become quite arbitrary. Even if we choose a particular recorded event, like the storming of the Bastille, ambiguity still remains. Is it the moment the order to attack was given? Is it the first shot?
Or do we just say that it is the whole bunch of things that happen collectively, and accept that there is a degree of ambiguity necessary. It’s like saying you’ll recognize it when you see it, but it can’t be defined.