I sure hope we get to access all of Baldur's Gate city; I think I left some diamonds in that djinn house near the docks, so I'd like to go back and pick them up.
The day/night thing is something I definitely want in BG III. At night there is more chance of encountering undead or roving thief gangs or Narlen Darkwalk. But on the positive side, stealth gets a bonus and if they do infra-vision correctly, that will also have a big impact on engagement ranges. I think there are also some moonbeam spells and the Ring of Shooting Stars that work best in darkness outside. I've always wanted that ring, but never got one.
