The only time I find my Sims on other clock time than I left them is when I have been playing other households. And I enter the household at the exact time as I left the previous household.
When I exit the game from a household and then go back to it later the time is the same there as I left it and my Sims are doing the same things they were doing when I left. Although sometimes I find them standing beside the object they were working on (f.i. the computer) or sleeping in (f.i. the bed) but as I unpause the game they jump right back to what they were doing.
I did a test on it a few days after I got the game and I found that if I do not pause it, I did find that sometimes (not always though) time has passed within a household when I finally got through the loading window.
But like as stated by a few here above I always, without fail, pause the game before saving and exititing and when I enter a household, it is paused at the time I left.
