I can't imagine it actually takes that long. You need to spend 15 minutes on each stage to get the Score Attack stuff done. The Time Attack rounds usually end pretty quickly. I think each stage only has one real, long time attack in which they give you something like 10 minutes to work with but they tend to back less than four. And then Darkness has some.
8-10 hours seems crazy to me.
“Justice is the crowning glory of the virtues.” ~Marcus Tullius Cicero