Amsterdam time: stating every hour on the local clock
Every hour in a booking thread is on the Amsterdam clock. Guests writing from another time zone should say so, since a six hour slip turns evening into dawn.
Most bookings for an event date are made from abroad, often weeks before the trip and often from another time zone. A request for nine in the evening, typed on the other side of the Atlantic, can mean nine by the clock there, which is three in the morning in Amsterdam. The fix is two words.
The habit
Give every hour in the thread as Amsterdam time, and say so: "nine in the evening, Amsterdam time". The reply confirms the hour in the same terms. That removes the only kind of mistake that can quietly ruin an otherwise well-planned booking, one that neither side notices until the day.
Summer and winter clocks
Amsterdam changes its clocks on the last Sunday of March and the last Sunday of October, which is not the same weekend as the United States. For a few weeks in spring and autumn the gap between the two is an hour smaller than usual. A booking for marathon Sunday or the dance event, both in October, can fall close to the change; state the date and the local hour, and let the reply confirm it.
The date as well
For bookings late at night, give the date as well as the hour. "Saturday at one in the morning" can mean the small hours after Friday night or after Saturday night. Writing the date removes the doubt. The booking page lists the other details a first message should hold.