London to Cairo
The clock moves whether or not you are ready for it. This works out by how much, and what a bedtime walked an hour a night would look like on the way there or once you arrive.
Cairo runs 2 hours ahead of London. To arrive already keeping Cairo hours, your bedtime has to move 2 hours earlier — from 10:00 pm to 8:00 pm, on your own clock at home. That is 2 nights, so the table below starts 2 nights before you fly.
| Night | Bed | Up | Moved | Sunset there on this clock | Sunrise there on this clock |
|---|---|---|---|---|---|
| Night 1 | 9:00 pm | 5:30 am | −1h | 4:48 pm | 4:45 am |
| Night 2 | 8:00 pm | 4:30 am | −2h | 4:47 pm | 4:46 am |
The gap
Cairo runs 2 hours ahead of London for most of the year. Both ends put their clocks forward for their summer and back for their winter, but not on the same dates, so in the days between the two changes the gap is an hour different. The planner above works from the difference on the date in its field, so for a trip in those days its figure is the one that applies.
What that asks of a bedtime
Taking the shorter way round the dial, the move is 2 hours earlier. At the planner's usual step of an hour a night, that is 2 nights of shifting, either before you fly or after you land.
This is clock arithmetic and nothing else. It does not know how you sleep on aeroplanes, it makes no claim about how quickly anybody adjusts, and an hour a night is a step size rather than a finding. Shorten the step in the planner if a smaller one suits you.
Going back
For the return leg, or for anywhere else, the planner takes any pair of cities.
Once you are there
With the clocks settled, the ordinary question comes back: what time to go to bed for the alarm you have set. That is the wake-time pages, which count in cycles rather than in zones.