A layover is the time between an arriving and a departing flight; near Schiphol its length decides whether an in-room booking is possible and how long it can run.
Airlines and passengers use the word loosely. Some mean any gap between two flights; others keep it for a gap long enough to leave the airport and call anything shorter a connection. For booking purposes the useful definition is practical: a layover is usable when it leaves time to reach a room, spend time there unhurried, and get back through security with margin to spare.
Start with the scheduled gap and subtract everything that does not bend. Leaving the aircraft and, for an arrival from outside Schengen, passport control. The walk or ride to the hotel, whether that is a building joined to the terminal or a shuttle out to Hoofddorp or Schiphol-Rijk. Check-in or a day-room handover. Then, at the other end, the return trip, security and, on a departure leaving Schengen, a second passport check. What remains is the window a booking can occupy. On a nine-hour gap that is often three hours or more; on a five-hour gap it may fall under ninety minutes, and sometimes there is nothing sensible left.
A layover room is always an airport-area address, so the booking is arranged ahead with a start time agreed in the thread, and half the fee goes before she sets out. Ninety minutes, EUR 270, confirms with EUR 135. Message as early as possible, ideally before the first flight leaves, with both flight times and the hotel area, and the office will propose a start that respects the second departure. The layover page covers the sequence on the ground, and transit hotel explains the rooms that make short gaps workable.
If the inbound runs late, the layover shrinks from the front. Tell the thread as soon as the delay is posted. A deposit is not returned when a booking is cancelled, but a request to shift the start within the same evening is a different conversation, and the office would much rather have it early than at the last minute. The cancellation policy explains where the line sits.
One hour EUR 180 through to eight hours at EUR 1,250. Forty to sixty minutes anywhere in the centre; the Schiphol airport hotels by arrangement.