This product (which is long out-of-print but purchasable in PDF form) includes rules for time manipulation, paradoxes, etc. It includes spells explicitly designed to cause paradoxes, such as the 3rd-level spell minor paradox, the more powerful 6th-level spell paradox, and the immensely powerful 9th-level spell major paradox. Chapter 6 is all about the consequences of using such magic and “guidelines” for DMs “to solve any problems that might crop up.” (See p. 64). Chapter 3 also lays out ideas for time-traveling adventures and some of the player-facing difficulties that result from altering history.
As for lore, the only setting-specific lore on time travel of which I am aware comes from Forgotten Realms, and is detailed in this Q&A. Chronomancer, meanwhile, contains setting-agnostic lore involving “Temporal Prime,” posited as “a pseudo-reality that permeates every plane of existence among the alternate realities,” which the authors suggest was previously mis-described in other D&D products as a “Demi-Plane of Time.” (See p. 4).