when is twilight hours
2. the period in which this light occurs. 3. the period of time during which the sun is a specified angular distance below the horizon (6Â°, 12Â°, and 18Â° for civil twilight, nautical twilight, and astronomical twilight, respectively) 4. any faint light. 5. a period in which strength, importance, etc, are waning: the twilight of his life.