Time for Magic — P. Katherine Barkley

Max Knight is the daughter of one of the most powerful wizards in the world, and her cousin Jax Knight is the son of the other most powerful wizard in the world. Their parents once saved all of magic and defeated the most evil wizard ever known. Now in the second book of the Hunter Academy series, Max and Jax find themselves facing down another terrifying danger that threatens to destroy their world. Things are changing at Hunter Academy, and not in a natural way. People are appearing and disappearing, history is changing, and the Knight cousins are the only ones who can see what's going on. It's up to them to figure out how to stop it and put things back the way they were, the way they're supposed to be, and find out who's behind it all. With no one else able to help them, Max and Jax turn to another powerful wizard, one who may be even more powerful than their parents. Still, their combined abilities may not be enough; for in order to repair the damage to history, they must break through what has long been thought to be a cardinal rule of magic: You can't use magic to travel through or alter time.