Even assuming 10 hours... 45 / 10 = 4.5 Shines per hour... that's one (and sometimes more than one) virtually every 15 minutes for 10 full hours. Which is with no `messing around` / doing things aimlessly / simply having fun throwing Mario around the areas taken into account. That is kind of creepy considering the sheer time "The Manta Storm" alone can take... must've been blue-coin`ing it rather a lot surely? I really am slightly surprised that's physically possible in the game.
Then again, rounding that out to 40 Shines, thats only around one third of them gotten, making 30 or so hours which is a good length for any game really.
Edit: Just reread this and really liked the sound of "Shines-per-hour". Call it a speed of play rating method... come on, say it... "Shines-per-hour!" Doesn't it sound nice?
