I am not sure that "mostly at night" entries should stay here, and I doubt that restricting this to horror makes sense really - the description goes into detail about why horror might use it but whether the trope works only there is a different question.
Always Night, as a title, sounds like a supertrope that could cover any number of genres or reasons for darkness. I'd be inclined to expand its meaning, and possibly make a more specific subtrope for Horror movies if anyone really thinks it necessary. However personally, I don't think there is enough of a distinction between nocturnal monsters in "horror" vs. "fantasy" or "science fiction" to necessitate making this genre specific.
Well, maybe not splitting it by genre, but by something else? Just off the top of my head, a horror movie would have it be night at all times for ambiance, while a video game might do it because it's easier to run graphics that way (similar to the famous fog trick that Silent Hill pioneered).
It shouldn't be split by genre, it should be split by how and why it's used.
In some works Always Night is used to make a work scarier(related to Nothing Is Scarier?), other times it just aesthetics, like in some Film Noir or Cyber Punk stories(sister trope to Cyberpunk with a Chance of Rain). Both if these would be "ambiance".
It could also be because of more technical reasons like simpler graphics in a videogame as mentioned in , but technical reasons could include hiding lower quality sets, Rubber Suits or whatever.
I would say leave the title alone, to reflect settings where it is in fact Always Night, and revise the description to include all the ways in which the Always Night trope is used—for horror, or to establish a mood, or maybe a setting like 30 Days of Night where it actually is always night for some reason. Prune the trope list of examples where it isn't actually Always Night.