A simple task of turning a time turner can be interrupted by a simple thing as a sneeze. This simple event causes a ripple in time which brings the two time travelers further back then thought possible. Like the wings of a butterfly that causes a tsunami across the ocean, the stream of events will change their known lives.
Hogwarts Hospital Wing 1993
"Three turns should do"
It only took Hermione a moment to understood what Dumbledore was trying to convey.
Dumbledore left the wing and locked the door. Hermione crept closer to Harry and reached down and pulled an impressively long chain with an odd object attached to it. Then she lowered part of the chain over Harry's neck and wrapped her arm around him, pulling him closer. Harry, completely bamboozled by his best friend's odd movements, could only provide a grand impression of a stunned mullet. Suddenly Harry had the urge to sneeze. And sneeze he did, loudly and violently. This explosion of force caused Harry to knock into Hermione just as she was meticulously turning the device three times. Unfortunately, there were vary many more turns made. This increase of speed and longevity of force caused the two teenagers to loose consciousness.