Not so much impossible as "no idea how it could possibly work". Very few things are definitely impossible according to science, one example being the perpeetum mobile.
But I digress.
Both the perpetual motion machine and time travel are for similar reasons impossible: the laws of thermodynamics. The perpetual motion machine is impossible by the first law, time travel is impossible by the second law. To achieve either, you need to literally rewrite the physics of the universe to do the exact opposite of what they do know, and maybe duplicate yourself to replace you who has stepped outside of the influence of negative time in order to ensure the past is the very past you remember.
Very easy to do in fiction, 'impossible' in the real world.
Which is very much why I said link to tvtropez instead of link to wikipedia >.>
In Rockman, it seems quite easily done, if your name is Wily or Light. Makes you wonder why this technology never appeared in the future. Not even Chronoforce controls time, apparently that's just the perception of time for robotic lifeforms (though certain game mechanics make this very questionable.) And who knows what Crystal Snail actually does to mess up your gameplay. TimeMan and Flashman on the other hand really do seem to manipulate time.