Forty to sixty minutes, counted from yes
The arrival window is the forty to sixty minutes between a booking being confirmed in the thread and a knock at a central Amsterdam door.
Everything written on this site about timing rests on one figure. Forty to sixty minutes from the moment a booking is confirmed until she is outside your room, in any central district, on any day of a weekend. It is a window rather than a minute on purpose, and the honest way to use it is to plan against the far end.
Where the clock starts
Not at your first message. The count begins when the evening, the length, the figure and the address have all been agreed and you have said yes, because only at that point is there a journey for anybody to begin. A thread that takes twenty minutes to settle has spent twenty minutes before the window opens, which is the whole argument for writing earlier in the day rather than later.
Why it does not shrink
Quiet streets do not shorten it. The window covers her getting ready and getting across the city, and only the second half of that has anything to do with traffic. An empty Friday morning and a busy Saturday evening land in much the same place, which is why the figure is written once and not adjusted per hour.
Two things outside it
Schiphol and the airport hotels sit outside the window entirely, and the journey time out there is agreed with you before the booking is fixed. The other exception is your own building: a locked street door, a lift wanting a keycard, a night entrance around the side. She can be at the address inside the window and still be standing outside it, so anything unusual about getting in belongs in the first message rather than in a phone call at the end.