Here's the test I've done so far (haven't found anything)
- Played another family and then made them visit your household around 10 pm --> instant freeze
- Deleted some of the members of the family and kept just one (two different tries) --> 9 pm frezze
- Moved out some of the members and kept just one (two different tries) --> 9 pm freeze
- Moved the family to a different house --> 9 pm freeze
- Played another family till morning --> no freeze
- Switch back to family after playing a different one for a while and then switch to your family --> no freeze until 9 PM came along again.
- Played another family on that lot --> no freeze
- Moved whole family to new save --> no freeze
So I guess there's three options (for the moment at least, I forwarded your save)
- Start a new game with your family (I've just tried putting them in a new save but I'm pretty sure you can also place the house). This means you'll loose your family tree and all other Sims (you could move those over as well but without the relationships, those are lost).
- Try if a backup still works. The game should make auto backups.
- Tedious and undesirable: Switch to another family shortly before 9 pm and then play in that family until <tbd> and then switch back to yours . but you'll need to do that every night.