Cancellation, refunds and the warning you give
What stays behind when an evening is called off depends on how much warning your message gives, not on how close the hour was, and damages never come into it.
Cancelling is a message in the booking thread, and the clock on that message is the only thing that decides the outcome. Nothing is charged as a penalty, and no cancellation leaves a couple owing damages to anybody.
The three lines of the scale
More than twenty-four hours before the agreed hour, nothing is retained and the advance half returns whole. Inside the final twenty-four hours with her still at home, half of the advance half is retained as fee already earned and the rest goes back. After she has set out, the advance half is retained in full.
Two things that cut into the last line
If the released hour is taken by someone else, the advance half comes back entire, because nothing was lost after all. If you can show the real loss was smaller than the sum retained, only the smaller sum is retained.
The case with nothing behind it
A returning client's same day hour or two inside the city carries no advance half, so the scale has nothing to act on. Called off before she leaves, it costs nothing. Called off while she is travelling, it costs the share of the fee her journey represents and nothing further.
Moving rather than cancelling
A working week rearranges itself, so the first change of date is free where the request lands more than twenty-four hours ahead and the new date falls inside a fortnight. A second move, or one asked for on the day, is measured on the same scale as a cancellation written at that moment. The booking terms work through the figures, and the guide to work dinners covers which evenings are worth holding in the first place.