I went through old blog posts last night to see what I got. I had taken Western Civ II and Social Sciences on a Friday afternoon, and American Gov. on Monday. I don't study on Sundays ("six days shall you labor and do all of your work..."), so I basically spent parts of Friday afternoon, Saturday, and the morning of Monday studying for American Government. I'd guess 8-12 hours total.

Naturally, if I had spent more than the probably 8-12 hours that I did study for it, I would have done better, but I was only shooting for a passing score.