Chronomancy, in real world occultism, refers to divination specifically orientated around locating the best and worst times to do... well, pretty much anything. In actual fantasy settings, it refers to a subschool of magic focused on manipulating time in various ways. Whilst this is mostly a /v/ phenomena, due to the way players can really, really fuck over a DM by exploiting this in gamebreaking ways on the tabletop, there are tabletop settings where it makes an appearance.
Arcane Exxet, the magic and supernatural sourcebook for Anima: Beyond Fantasy, features Time magic as an available subschool.
Dungeons & Dragons
Time magic has made rare and sporadic appearances through the history of Dungeons & Dragons. Usually, when it does appear, it is in the form of individual spells or, more rarely, psionics that provide some limited ability to travel through time. The spells Haste, Slow, and Time Stop have appeared in most editions. It can be argued these don't actually manipulate time so much as let the effected creature move really fast (or slow in Slow's case). In 3rd Edition, the spell Teleport Through Time appeared in a web article on WotC's official website. Theoretically kept in check by requiring a very specific material component, it became spectacularly broken because it neglected to prohibit Eschew Material Components from bypassing that need. A handful of Psionic abilities comboed to allow a clever user to rewind time, which is detailed below.
The "Psionic Save-Game" exploit in 3.5 combined the psionic power Time Hop, from the core psionics book, with the power Forced Dream from Magic of Eberron. Time Hop propelled the target forward in time a few dozen seconds, an action normally harmless to the timestream and functionally identical to the common Maze spell (except it didn't take time away from spell duration), while Forced Dream allowed the user to rewind time to the start of their turn. On its own this combo was a nice trick, but combined with a few other pieces the time between save and load could be extended to days.
In 4th edition, a ritual in Dragon Magazine allows the caster to open portal to different times, thus allowing for time travel as a semi-controllable plot element.
Outside of these dabblings in temporal magic, D&D has rarely gone into depth with allowing a player to fully exploit chronomancy. The first attempt at a full-fledged time manipulator appeared in the form of an NPC class for Advanced Dungeons & Dragons 1st edition called the Time Lord. Then 2nd edition debuted a splatbook called "Chronomancer", which gave players the ability to play a Wizard specialist focused on time manipulating magic. After this, time control slipped out of players' hands until Dungeons & Dragons 5th Edition, where the "Chronurgist" is one of the Wizard subclasses based on Dunamancy, focusing specifically on its time-manipulating aspects.
- Ability Score Requirements: Intelligence 17+, Wisdom 16+ (to dual-class to Chronomancer requires Int 18+ and Wisdom 17+)
- Alignment Requirement: Non-Chaotic
- Race & Level Restrictions: Human (Unlimited), Elf (15th level), Half-Elf (12th level)
- Chronomancers gain +1 spell per level, which must be a Chronomancy spell, as with any specialist wizard.
- Chronomancers do not gain any saving throw bonuses against Chronomancy spells, although they do still inflict a -1 penalty to saves against them.
- Prohibited Schools: Abjuration, Conjuration/Summoner, Necromancy
- -2 penalty to saves against spells from prohibited schools being cast by specialists in those schools.
- +10% bonus to learning Chronomancy spells, -25% penalty to learning any other spells.
- At 5th level, become immune to Haste and Slow spells.
Compared to wizards, Chronomancers have a unique EXP to level table, but otherwise they're basically just their own kind of specialist wizard.
Chronomancers have access to four kits and two subclasses. The kits are the Guide (a Chronomancer working to coax history along a path of their choosing), the Historian (a Chronomancer using magic to better study the past), the Seer (a Chronomancer focused on studying the future), and the Traveler (a Chronomancer who wants to master the practical aspects of time travel and basically treats the past & present like dungeons to raid in the process). The subclasses are the Temporal Champion, a Chronomancer gish who trades some of their spellcasting oomph for more warrior-like martial abilities, and the Temporal Raider, a Chronamancer turned thief.
Worldbook 3: England for Rifts features both Temporal Mage and Temporal Knight character classes.
The rare and much maligned True Brujah bloodline from Vampire: The Masquerade can control time with the Temporis Discipline.
Wraiths may gain some control over the passage of time using the Pandemonium Arcanos in Wraith: The Oblivion.
Characters in Changeling: The Dreaming can control time using the Chronos Art.