1) The time limit is in place to facilitate change in the world, as well as to drive the player's adventure. Each individual day as no time limit. Instead, a player chooses whether to advance to the next day by sleeping in a bed. Therefore, players are encouraged to check on things as time passes. For example, new characters may appear, and areas may open or close. Toward the end of the 50 days, the player should really be able to relish in a sense of impending doom.
Okay, that sounds cool! Kind of like a soft time limit? I'd hate to see an exploration game slip by because a hard time limit was tick-tocking away...
Also, since everybody is talking about darkness, Imma chip in a bit. Remember Dark Souls 1? When I think about it, that game didn't really have that many dark areas. Yup, you can quote me on that.

The overall feeling is like you're trudging through dark forests, marshes, caves, and catacombs, sure. But they weren't actually dark - in most places, you could see around pretty well. So, how did they do it, if not by actual lighting?
They used a lot of muted and cold colours, for one. Even well-lit places, like Firelink Shrine, were made predominantly of cold blues and greens. Grayscale, too, of course, and earthy browns. Don't remember many maps with warm colours - Izalith, yes, and the Demon Ruins, but they were peppered with black and grey, too. Anor Londo, yes - but there the warmth is, for all its splendour, kind of washed-out. That's not just colour-work, either. The sheer size coupled with the sheer emptiness made it feel abandoned and forlorn.
Another thing they did was contrast. DS1 was never all black. Like, remember the Catacombs? That was dark and sucky. Except, sizable parts of it were actually open, airy, and flooded with icy blue light! How about that? The dark parts seem all the darker when they transitioned into areas that weren't dark. Conversely, when FromSoft did a thing that was all dark (damn you Bloodborne!) it wasn't half as exciting.
Soo... dunno what you can glean from that, but hope it helps a bit!