Try AD&D 2e's obscure product Chronomancer.
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).
Finally, for the sake of completeness, in 3e/3.5e there were a few less-helpful, less-detailed, and in some cases less-official references to time-related gameplay:
- The 3e Manual of the Planes presents a "variant plane" called the "Temporal Energy Plane." Its description mentions time loops, but not time travel or paradoxes per se. (See p. 208-210.)
- An article on Wizards of the Coast's website entitled "Perilous Gateways:
Portals in Time" sets out a teleport through time spell that provides a mechanism for time travel. The article goes on to warn the reader about paradoxes and offers the hand-wavey suggestion that "it is simplest to use the rule that changes in time are minor and somehow time smooths them out."
- Dragon Magazine #350 presented an article on "Chronomancy," which included the statement that "Currently, no spell, artifact, or creature in D&D can time travel over a span of years." The time-related mechanics presented in the article do not permit time travel per se. The article suggests that time travel might be "the purview of deities of travel and time[.]" (See p. 76-79.)
- Dragon Magazine #359 included a write-up on a monster called a "time dragon," the Great Wyrm form of which has a Time Apotheosis ability that permits it to travel backward and forward through time more or less arbitrarily. The material does not engage the possibility of paradoxes.
- There were a couple of psionic powers, such as the 9th-level power time regression (Expanded Psionics Handbook p. 138) and the more limited 3rd-level power forced dream (Magic of Eberron p. 104) that allowed the user to move backward in time by very small increments, which theoretically might be capable of creating paradoxes. None of that material explicitly addressed how such paradoxes might be handled.