The in-game timer’s broken. It records how long you’ve been playing, but it doesn’t pause the timer when you close the DS, which is what I’ve been doing, instead of saving and quitting.
So, apparently, it’s taken me 330 hours to get to midway through chapter 8.
Tim's Gaming Diary 
Yes, I noticed this when I found it had taken me 41 hours to complete the game. Slightly annoying.