Is it just a visual thing? Or does it affect gameplay?
Obviously, there is no point in introducing day/night cycle if it did not influence everything especially in the D&D setting where day and night make a huge tactical difference as you write. IMO, the game would not have needed the cutscenes but the voice acting and narrator would have been sufficient. I would have rather focused the resources on tactical gameplay elements and the atmosphere such as the D/N cycle. Obviously, I am not deciding about these things and am likely to represent a minority. It might be a lost cause unless Larian decides to go for it. It would not be the first time they would do a crazy effort to make their game better. They are a large studio now capable of doing large undertakings if they so decide.
Light influences how we perceive things. Those vampire encounters on a graveyard in BG2 were epic because they took place in the night. Comparable graveyard scene in D:OS2 was not memorable because it took place in the middle of the day or at least you would not have to time it and wait for the night.
