One would say, there is a liminal -- Latin, meaning threshold -- period that clearly separates before and after.
Flying over the large capital, Kathmandu
Landing onto the Tenzing-Hillary (Lukla) Airport, which is scary enough to be almost always a signal, for the visitors, to start their journey.
Looking up the Himalayan mountains on the way to Thukla (4600 meters)
It is my argument, however, there CANNOT be a period of such, that distinctly separates two different phases and that a person can grasp into his mind. This is rather a philosophical thought, against most structuralist theorists. I will return to this theme later.