Wow! Felt like it ended too soon.
Only if you could have done a little work on the end, as an extended conversation between both JEFF about the Time Machine which could have given more details about future Jeff.
Another point is, if future Jeff is just 3 years later version, why he doesn't remember Sarah or Keziah or Chris? Is there any backstory? If yes then it would have at least hinted during the ending conversation.
Overall it's funny. Good premise, engaging writing.