Homer’s first time travel was part of the fifth Halloween montage in a segment called
“Time and Punishment” (aka “Homer’s Time Travel Nightmare”) where each tiny
dinosaur he stomps on alters his own life. The next bit I saw was Professor Frink, who built
and used the chronotrike in “Springfield Up,” attempting to tell his young self to choose
a different career.
Homer: (to self) Okay, don’t panic!
Remember the advice Dad gave you on your wedding day.
Grandpa: (in flashback) If you ever travel
back in time, don’t step on anything, because even the slightest change can alter the
future in ways you can’t imagine.
1 English variant