The arrival window, for someone new to the city
The arrival window is the forty to sixty minutes between a confirmed booking and her knock on a door in central Amsterdam, at any hour of the day or night.
The arrival window is the time between the moment a booking is confirmed and the moment she knocks. In central Amsterdam it is forty to sixty minutes, and it stays the same at breakfast time, at midnight and at four in the morning. It is counted from confirmation, not from the first message, so a quick reply on your side shortens the wait.
Which rooms it covers
The window applies across the centre of the city: Centrum, the Jordaan, Oud-Zuid, De Pijp, Zuidas, the streets around Leidseplein and Rembrandtplein, Dam Square, the edge of the Vondelpark and the Red Light District. A first-time visitor rarely knows which of these their hotel belongs to, and that does not matter; the street address in the message is enough to tell.
Where it does not apply
The hotels around the airport sit outside the window. A room at Schiphol, Schiphol-Rijk or Schiphol-Oost is arranged separately, and the journey time is agreed with you before anything is fixed rather than quoted as a standard figure. If you are unsure which side of that line your hotel falls on, the airport hotel or city hotel page sets the two out side by side.
A practical habit
Plan on sixty minutes rather than forty. A shower, a lamp switched on in place of the ceiling light and a phone kept within reach are all that is needed before the knock.