I found a screenshot showing that Throne of Bhaal did have day & night ... here is Saradush:
you can see the little time pendulum in the lower left corner, with the night moon waning and the sun coming up soon.
The night time version of Saradush was scripted. It was only available after completing a certain quest. The completion of that quest allowed you to click on the night time version of the city (On the map it was Saradush with a crescent moon)
There was no Day/Night cycle in TOB, just a scripted version of Saradush at night where a specific plot event occurred.