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 don't find the lack of day/night essential, and the reason you give seems sound. But, if every board/act didn't take place in the daylight, then extra scripting wouldn't need to be done. For example, Arx could have been in a night time setting without having a need for any more scripting and assets than was needed for the day (maybe even less). Just a little variety .
That could still happen. Making a map perma day and perma night is not a cycle. They only said there would be no time-changing cycle.
