I'll be convinced otherwise only if a non-player character gets mad at you for having kept them waiting for a whole day; time that passed while you, the player, was away from the computer while leaving the game running.
Well they already don't get mad at you for spending hours and hours doing other things, so I'm not sure how the day/night cycle is worse.
I think the thing of it is, time is passing either way. Some people feel that the day/night cycle is too obvious, and breaks the world. But I would argue that it isn't breaking anything that isn't already broken, and that it's fixing minor things (like the lack of any in-universe time mechanism).
That's fair. Although I liked how DA:O too place over the course of a year, according to in-game dialogue. You could beat Skyrim in around five (in game) days if you mapped things out perfectly. Such things seem a little silly to me.
But I get what you are saying - you could easily not solve the main quest in Skyrim for, literally, years. I just find the day/night cycles to demean the passage of time in my perspective, not enhance it.
While i'm not disagreeing about DA:O, literally the only place I recall mentioning that is Wynne's conversation. Which is just weird. Like In Exile said, there are no other signs of passing time. I'd argue that a day/night cycle allows that.
And I might not have been clear enough with my example about *time passes*. What I meant was, you could have a certain mission that ONLY happens at night. And thus, whenever you start the mission, you either have some kind of fade out/fade in to the new time, or an actual scene of time passing. This shows that time has moved, and allows the game to (albeit somewhat artificially) extend the actual play time beyond three days.
You could also do it with bigger plot points. After, say, resolving the Templar/mage conflict in an area, when you begin the next main quest, a character could reference that event as being in the past. "It's been a month since we resolved the conflict in the Hinterlands, Inquisitor, and [the mages/Templars have not caused any trouble] / [the Templars and mages are working together]."