Last light, in Sol's words, is civil dusk: the sun 6° below the horizon, the end of the light you can work by and the end of blue hour.

After sunset the sky keeps lighting the ground for a while, and Sol names the end of that usable light rather than the moment the disc goes. In the outing it is the last of the three times that matter — arrive by, sunset, last light — and the plan's calendar event runs to it.

The sunset outing plans around it — arrive by golden hour, and the colour, when it comes, arrives before last light.