Batman: Arkham Origins Initiation DLC, I Am The Night mode detailed

[Grievous]

I think they expect you to sit for 12 hours and finish the game. It is like an 'insanity' mode type thing.

I really doubt it, I think its going to be more like Ironman mode on Xcom. Even dead space where they expected you to sit the whole time had 3 save points in that case (so you could split it up by 3-4 hour sessions), and it was a shorter game by the sounds of it.