The Age of Miracles by Karen Thompson Walker

Eleven-year-old Julia lives with her parents in southern California when the event occurs that everyone calls “the Slowing.” The earth begins to rotate more slowly, which means that days last longer and the night/day cycle no longer matches clock time. Julia's world is affected immediately when her best friend, Hanna, a Mormon, moves to Utah with her family. With no close friends, she spends her time thinking about her skateboarding neighbor, Seth Moreno. Her parents also try to maintain some sense of normalcy despite the growing uncertainty of what's going to happen. They decide to follow the government's suggestion to follow “clock time” (based on the 24-hour clock) rather than “real time” that now has days lasting more than forty hours. But when animals start dying and tensions erupt between the clock time and real time people, it becomes harder and harder to believe that the situation can ever improve. By setting a traditional tween's growing pains against the backdrop of a global disaster, The Age of Miracles is a very different and compelling coming-of-age novel.