Chronomancy is the art of manipulating time in some form or another in magic and those who specialize in using it exclusively are Chronomancers.
A chronomancer can manipulate various aspects of time, from a person's perception of time, stealing memories, stopping aging, progressing aging, extending someone's life, and even reversing time itself. However, using this art requires precision as the slightest mistake will have severe penalties for the user, including losing years of their life or instantly aging to dust. Thus chronomancy deals with protection and the immeteria.
The method of using chronomancy varies, but the most well-known is through the use of Zeitgeists and various runes, which indicates it has a foundation in Shamanism. Alternatively this means that they can tap into Shamanism.