Is there any meaning to the passing days?

Solution 1:

For the most part no, however some quests will require you to be present in a given location at/around a certain time of day/night. And you can't, for instance, hunt nightwraiths at high noon (or noonwraiths at midnight), and most villagers will sleep during the night and work during the day, and so on.

And of course, if you go to sleep for 16 hours when you're supposed to be protecting the burial detail from necrophages there will be consequences (such as failing the quest because, you know, everyone got eaten while you were having your nap). You can fail some active quests by taking too long, going to sleep, or otherwise wandering off when important things are happening. But those situations tend to be obvious, and are the exception rather than the rule.

But in terms of whether or not the passage of entire days/weeks/months makes a difference? No. Except your beard will get longer.

Solution 2:

Basically, there are no sideeffects. Sometimes, you even have to wait because a quest is only available at a specific daytime or after a couple of hours or some monsters only spawn at a given time.

However, the only problem I've seen was that a quest failed. I've encountered a random merchant with his cart who asked me to burn the corpses around him. Somehow, i forgot that, went away and waited because I needed new potions. The quest failed after that, but this was the only drawback I had because of that.

Solution 3:

There is a quest now in the Add-On "Hearts of Stone", where you only have a limited time.

Careful Spoiler:

Whatsoever a man soweth