Aviation solved the time zone problem decades ago by refusing to use local time at all. Flight plans, weather reports and crew schedules all run on UTC, one clock for the whole planet, and pilots convert to local time only when a passenger needs to hear it. Travellers do not have that luxury. Your ticket prints departure in one local time and arrival in another, your phone switches silently when it finds a network, your laptop calendar often does not, and somewhere in the middle of all that you are booking across time zones and typing a start time into a message. It is a surprisingly good way to be an hour out.
What time Amsterdam actually keeps
The Netherlands runs on Central European Time, one hour ahead of UTC, for the winter half of the year. From the last Sunday in March until the last Sunday in October it runs on summer time, two hours ahead of UTC. That means the gap between Amsterdam and your home city can change during the year, and not always on the same weekend as your home clocks move. Travellers from North America in particular meet a few weeks each spring and autumn when the usual difference is off by an hour.
For a booking, one rule removes all of this: write the start in Amsterdam time and say so. The reply confirms the start in Amsterdam time too, so there is only one clock in the thread.
Booking across time zones: the phone, the laptop and the watch
The error usually comes from a device, not from arithmetic.
- The phone normally switches to local time after landing, but not always straight away, and not if automatic time zone setting has been turned off.
- The laptop often keeps the home zone, and so does the calendar on it. An evening block that says 21:00 may mean 21:00 somewhere else entirely.
- The watch is whatever you set it to on the aircraft, which after a long night may be neither home nor here.
Before writing a start time, look at a clock you know has changed: the phone's lock screen after it has been on a local network, or the clock beside the hotel bed.
Twenty-four hours, not twelve
A message saying nine is a coin toss. Nine in the morning or nine at night, and in which zone? Write 21:00. The twenty-four hour clock is standard across Europe, it is how the reply will be written, and it removes the most common misreading in one stroke.
After midnight, name the date
The second classic mistake belongs to late bookings. A traveller writes on Tuesday evening asking for one o'clock tonight. Is that the first hour of Wednesday, a few hours away, or has the traveller's own day already ticked over at home? When a start falls after midnight, give the night rather than the date: 01:00, the night from Tuesday into Wednesday. It reads slightly formal and it is never misunderstood. Bookings in those hours are ordinary here, and the note on the hours of the clock explains why they are often the easiest to arrange.
The two nights the clock changes
Twice a year Amsterdam's clock does something odd, and both happen in the small hours of a Sunday.
On the last Sunday in March the clocks jump forward from 02:00 to 03:00. The hour between does not exist. A booking asked for 02:30 that night has no meaning, and a two-hour session starting at 01:30 ends, by the wall clock, at 04:30.
On the last Sunday in October the clocks go back from 03:00 to 02:00, so that hour happens twice. A start at 02:30 could mean either of them. If you are booking through that night, give the start in relation to something fixed, such as an hour after you land, or say first or second 02:30 and expect a smile in the reply.
Using your landing time instead
If you are still in the air, the cleanest solution is to avoid clock time altogether. Send the flight's scheduled landing in Amsterdam time and ask for a start relative to it. The midnight arrival guide shows how a booking can run in parallel with the arrival, and it works just as well from a departure lounge five time zones away.
The body is on yet another clock
Even with the right Amsterdam hour in the thread, your body will disagree with it for a few days. That is a separate question, and it is worth reading the jet lag page before you choose which hour to ask for. The written start should be correct in Amsterdam time; the choice of start should suit whatever time your body thinks it is.
A message that cannot be misread
Hotel name, then: 22:30 Amsterdam time, tonight, ninety minutes. Or: 01:00 Amsterdam time, the night from Friday into Saturday, one hour. Confirmation comes back in about ten minutes with the same clock, a name and an arrival. The rate does not change with the hour: EUR 180 for sixty minutes, whichever time zone you started the day in.