Bah, I just want to know about how much, it doesn't need to be precise.
And yes, it is true that scoring possibilities on Dark missions are infinite, but that is reaaaaaally cheap and evil (and, fyi, only works on certain stages with specific traits). I don't do that, and in the fear that it will be used here, I will try not to mention it ever again, unless I say we should have a rule against it.
Anyway, I need to know so I can perfect my score on Lava Shelter's Hero mission, which I am obsessed with for some reason. I know that I could probably decrease my time by a few seconds if I tried hard enough, so that's my reason for needing to know at least an approximation of how much time factors into your score...