While allowing the party to be split up, with some in real time and some in turn based combat, does cause issues with syncing a day/night cycle, that isn't really critical.
The main problem is just the added complexity for doing a day/night cycle properly, on top of already complex scripting and narrative. With level design every NPC needs a place to go at night, those places need contents, etc.
I know larian is maximalist, but still I would not even mind a less complex day and night time cycle. Seeing people going to bed, is not something, what I would miss...
If you do not meet the kids in bigger cities and some specific characters at night, that is enough for me. So some streets, become a bit more emptier.
They go to sleep using their own "waypoints", when not seen on screen.
Weather effects could be something very rare. Rain could cause wet on characters for many turns or just a couple of very-very small spots on the map if any,
to avoid too much elemental effects...
In DAO2 some places are just always very-very bright, that is a way more stranger for me, than seeing, that people not sleep at night in their own apartment...
