Larian had already begun work on the day/night cycle before deciding to drop it, so the code for a cosmetic nighttime is already in the game and should be easy to activate by mods.
They stated that they hope to support the game after release with more content and bug fixing patches, but the extent of the support will depend on the sales. There probably won't be much support in the first week or two after launch, however, since much of Larian will be going on vacation.
