"They were at the edge of the Twilight Zone." (David Falkayn: Star Trader, p. 156)
On Earth, dawn, morning, noon, afternoon, evening and night are a temporal sequence whereas, on Ikrananka, they are places. A planet observed from space is seen to have permanently lit and unlit sides, especially if the axial spin is disregarded. Sunrise or sunset can be made to seem permanent by someone who flies above the planet at just the right height and speed. Can a time traveler reduce his speed to zero and thus witness a single moment permanently? The Wellsian Time Traveler's "speed" is, e.g., one subjective second per one objective millennium. Can he go into reverse, e.g., one subjective millennium per one objective second? Thus, he would die of old age and disappear in an instant? He would be able to spend the remainder of his life watching a single sunset.
I am trying to think of different possible meanings of the phrase, "Twilight Zone."