Discworld
Discworld humor either bites you or it doesn’t—not so much for me, but my friend Jim Martin talked me into reading The Last Continent (1998) for its send-up of “The Sound of Thunder” and the grandfather paradox. And I did laugh. I can’t guarantee that that book is the first time travel in Discworld, but it does precede the other time travel that I know of in Night Watch (2002).
“It’s not just that things in the future can affect things in the past,” he said. “Things that didn’t happen but might have happened can. . . affect things that really happened. Even things that happened and shouldn’t have happened and were removed still have, oh, call ’em shadows in time, things left over which interfere with what’s going on.” 
