Full Idea
Lewis says a journey only counts as interesting time travel if there is a disparity between personal time and external time. …It is also necessary that the person at the beginning of the journey is the same as the person at the end of the journey.
Gist of Idea
The interesting time travel is when personal and external time come apart
Source
report of David Lewis (The paradoxes of time travel [1976]) by Baron,S/Miller,K - Intro to the Philosophy of Time
Book Reference
Baron,S/Miller,K: 'Introduction to the Philosophy of Time' [Polity 2019], p.194
A Reaction
Other cases would presumably be the whole of time accelerating or slowing, or going into reverse.