Blue hour, 20s, f/8Streetlamps warming upLast colour on cloud
The half hour that is actually worth waiting for
Most people pack up when the sun goes down, which is roughly twenty minutes too early. Civil twilight is when artificial light and sky light are close enough in brightness that a single exposure can hold both. Miss it and you are choosing between a black sky and blown windows.
Metering when there is nothing to meter
Matrix metering has no idea what to do with a scene that is 80% dark. I meter off the brightest patch of remaining sky and pull back two thirds of a stop, then check the histogram rather than the screen — at this hour the screen lies, and it lies in the flattering direction.