Yeah I figured that's how it worked. Time isn't frozen in this game. Time keeps going on regardless if you are playing that lot or not. In fact, if you are having issues with bills you can choose the richer families to take the hit lol by leaving the game on sunday when its the "poor" family's lot then playing a rich sim through monday. Then leaving the rich family and coming back to your poor family. Bam you skipped the bills. Aging itself is frozen unless as you said you hop over some line in which you might lose 1 day. That "line" doesn't feel consistent to me either. IDK. I always try to leave my lot/houses in the early morning like 5am or 6am now.
