Twilight light lasts for only about 30 minutes when the sun is at or drops below the horizon. This 30 minute time span is also known as “The Golden Hour” in photography. During this time the light is softer and warmer in hue. When the sun is below the horizon the light travels farther through the atmosphere reducing the intensity of the direct light and the illumination mostly comes from indirect light therefore reducing the shadows.
These shots were taken using a 4x neutral density (ND) filter, which reduces the exposure by 4 stops. Using an ND filter allows you to use a slower shutter speed by reducing the amount of light going through the lens to the camera sensor, thereby allowing movement to blur. When you attach your camera to a tripod you fix the non moving elements in the image and the moving elements (the lake water here) take on an ethereal look.