Henry Ford Museum

In my opinion, it takes a good day to see the museum reasonably thoroughly and a second good day to see Greenfield Village reasonably thoroughly. That doesn't mean reading every sign or necessarily seeing every last exhibit, but it should give enough time to cover most things at least briefly and linger at some things that are of greater interest. Needless to say, people differ in how rapidly they go through a museum, so that's at best a very rough guide. I assume the factory tour is more of a fixed length thing, though I haven't done that myself.