Sentence:  At <WSD>twilight</WSD> in the summer there is never anybody to fear—man, woman, or cat—in the chambers and at that hour the mice come out. They do not eat parchment or foolscap or red tape, but they eat the luncheon crumbs. 
Meaning of the word marked with <WSD> tags:  The time when this light is visible; the period between daylight and darkness.