The arrival window, and where the airport sits outside it
The arrival window is the forty to sixty minutes in which a therapist reaches a central Amsterdam room after confirmation; airport rooms are arranged instead.
An arrival window is the span of time between a booking being confirmed and a therapist reaching the door. For central Amsterdam it is forty to sixty minutes, and it holds at any hour. A traveller who writes from a hotel in the Jordaan at half past eleven can expect a knock between ten past and half past midnight.
Why a window rather than a minute
Journeys across a city vary. A bridge opens for a boat, a tram blocks a narrow street, a hotel entrance takes longer to find than expected. A window of twenty minutes absorbs those variations without the guest having to wonder whether something has gone wrong. When she is close, the thread says so, and when she reaches the building it says so again.
The airport is not in the window
Rooms at Schiphol, Schiphol-Rijk and Schiphol-Oost sit outside the standing window. They lie beyond the ring road, the journey depends on the hour and on where she sets out from, and a fixed window could not be promised reliably. So an airport booking works differently: the house agrees her journey time with you, and a specific start is confirmed on that basis. Instead of a window, you have an agreed time.
Why that suits a late landing
A traveller in the air cannot know exactly when they will be in the room, and a window counted from confirmation would start running at the wrong moment. An agreed start, fixed against the landing and the time needed to clear the terminal, suits the situation better. If the landing slips, the start can move while she has not yet set out.
Moving between the two
A traveller who spends the first night near the airport and the rest of the trip in town will meet both systems. The first booking is arranged with an agreed journey time and half ahead; later bookings in the city run in the window. Back in town, a client the house already knows who wants an hour or two later that day settles the entire fee on arrival. The guide to journey times sets out the differences in full.