I think it largely depends on why the person chose to time travel in the first place. Unnecessary impatience and item/bell exploit of the internal clock feature are the two things most people really frown upon. It can be justifiable, I think, but only in particular situations where you couldn't otherwise wait to be rewarded.
I don't agree with time traveling forward a day to finish a public work project, as that's absolutely just impatience. It's giving you an advantage over players who otherwise would not have been rewarded yet. The game doesn't ask you to wait a day for a bench to be built or a week for a shop to open just for you to fiddle with the clock and get instant gratification, it makes no sense and it is deliberately going against the system and storyline provided.
It isn't even debatable that that is indeed taking advantage of the internal clock tool. It's whether or not that is a bad thing that starts discussion like this.
I don't think it is necessarily "cheating"(at least, not on a big scale) unless you're skipping months at a time for bells or exclusive items, but it definitely shows impatience if you get a lot of time to play during the day as it is. It's frustrating to those who wait because it shows an inability to walk around, see what's going on, just be in your own little synced world and have a nice time -- all of that is a huge part of enjoying an Animal Crossing game to the majority of loyal players.
That being said, no one should have to be made to feel guilty for trying to enjoy the game with a full-time job, kids, demanding school, etc. It's just not realistic that they are going to make good progress in the game without at least some time travel here and there, so it makes sense to alter the time to fit their real-life schedule.
I just don't think it makes sense to rush a game like Animal Crossing only because you can. I believe there's a definite line between "playstyle" and just wanting instant gratification, and how people look at your time traveling depends which side you sit on.
They don't have an advantage over anyone. The people who wait are more than able to time travel if they want.