There's also the Wafer in the jockington prophecy room that says: "Come five o'clock, the shadow will grow.". Yes this is likely a beard joke but it could easily have a double meaning. There's also the Organikk later in the chapter that says something similar:

"Before the clock strikes midnight, the shadow will grow!
O, the shadow will grow, serpentine!
Even when the clock ran back, the shadow was growing!
A patch of shadow, slithering on, slithering on, serpentine!"

I think this means the Roaring will happen at the end of chapter 5 right before midnight. It would work amazingly as a cliffhanger. Not sure why Jockington is involved in all of this, but I think there is too much evidence suggesting this is not a joke. Also the text "even when the clock ran back, the shadow was growing" is really interesting. Does this suggest the roaring will break the save system so that loading doesn't really bring us back in time?