This creature hunts only at night.
Bored now. Daytime is the worst. Cooped up for hours. Can't hunt.This is for when a species of animal or monster, usually a Super-Persistent Predator or another highly dangerous beasty hunts and kills only at night. For whatever reason they don't go out during the day, at which time they tend to sleep or prowl their darkened Evil Lair. It's not that they're Weakened by the Light (though that can be a prime cause for this trope), it may just be simple lifestyle, biology, or a tactical choice to hunt better. If the heroes are out hunting this Nocturnal Nasty and go Exploring the Evil Lair, then there's likely going to be a scene where they beat a hasty retreat into a sunny area where the creature dares not tread. If it's sunset, then the tension will ramp up as it slowly draws nearer to the heroes or closer to rousing. See also Diurnal Nocturnal Animal and Nocturnal Mooks.
-- Vampire Willow, Buffy the Vampire Slayer episode "The Wish"