Yeah, I agree - the only timed NPC mission I remember is with one who tells you outright he wants to look for his witch, and there are tricsk to prevent him from leaving if you don't complete it in time or don't want to (so you can reload a save if you find out too late), and the other two who tell you they want to go to a certain place never actually leave even if you don't go to the Naskhel mines (I think it was intentional and not a bug). Given that you're given weeks or months to complete the quest for Dynaheir, it's not really that much of an issue and it's actually fun that the game does have a limit and it's not a static game.

I haven't finished the game, so I'm not sure if you're talking about the endgame now, but at least until middle of the game there aren't any points of no return, and since you've already let the OP about the potential issue, they can always ask you for a hint (eg. don't start the quest a NPC called X gives you or you'll start the timed quest/save before it). I've actually read a walkthrough of the game, so if I remember correctly, the only point of no return is basically at the end of the game and it's pretty much obvious it might happen, so like teceem says, it shouldn't be an issue.