Peak dates, and booking a trip around them
King's Day, Pride, the dance event in October, Christmas to New Year and large conference weeks all carry a deposit whatever the notice given.
A peak date is one of a small set of periods when the city fills: King's Day, Pride, the Amsterdam Dance Event, the stretch from Christmas to New Year, and large conference weeks. The house names any of them when asked.
What changes and what does not
The fee does not change. An hour for the two of you with one therapist is 360 euros on King's Day exactly as on an ordinary Tuesday. What changes is that a peak date carries half the fee ahead whatever the notice, and that availability across the roster narrows considerably.
Why it matters to a long-distance couple
Because the flights are usually bought against price, and the cheapest weekend is sometimes the busiest one. If your dates land on a peak period, arrange the evening in the same week as the seats rather than later. The woman the two of you agreed on is much more likely to be free eight weeks out than eight days out.
Rooms as well
A central room on a peak weekend is both more expensive and harder to find, which pushes some couples towards an airport hotel. That is possible by arrangement, with the journey time agreed first, and it carries a deposit like every Schiphol booking. Say it at the first message rather than at the end.