Well if you have played the game past the first hundred years or so, you'll know it slows down to a crawl after a while. So trying to answer this question, since you have to take into account the game gradually getting slower and the sheer impracticality of playing it at full speed (unless you're playing observer mode), and the fact that the game will run differently on different rigs...
So to make a long answer short, exactly twelve hours, for all three scenarios.
Edit: Actual answer, it used to be like forty-ish hours, I believe? Actually playing a campaign with stopping, mind. It's been a while since I played to the end of time.