When I tried to send my mix to her parents' house before 4:00, the option was greyed out. But then I sent her to the day care, and she can go there. Why is that happening?
I tried with my 20th Anniversary M!x just now (3:32 PM local time) and I can access the parents' house just fine.
The only thing I can think of at the moment is that it is disabled because one of the meters (hungry/happy) are empty. At least that's what the manual states.