I don't know what benefit would come from a 12 hour jump but you can use the ->l button to jump 24 hours in the guide.
I just left DirecTv and came back to Tivo after about 7 years. I loved that 12hr jump.Does anyone agree with me that a 12 hour jump ahead button on the TV grid would be nice? Just came back to Tivo after years with Directv. They had this feature on their DVR, and it was nice. Just a thought.