Okay, I went back to Hiro attacking Sylar. Just before Hiro attacks, Sylar's eyes turn, and then his mother falls - indicating that time started up again. So whether this was caused by Hiro ceasing to use the power, or Sylar intervening in the use of the power remains to be seen.

Now, to go back and look at the cheerleader sequence I was talking about...

Okay, Episode 9 (Homecoming), Part 5. I don't know where the pictures are, but the picture of Claire on the steps of the auditorium showed her turned around, with one shadow looming over her. In the TV episode, Peter catches up to her, and both of them are under the steps when Sylar's shadow falls onto them. Maybe it's just a gaffe, but I think this is where Peter caused a major change from one possible future (Claire is killed) to another (Claire is saved.) Obviously, she was killed at some point, otherwise future Hiro's warning from the future wouldn't be necessary....IMHO.