In theory I think a closed system undergoing completely reversible processes could be considered perpetual motion (being reversible, entropy never increases). The second law states that those are the only sorts of isolated systems that don't gain entropy over time.

https://en.wikipedia.org/wiki/Second_law_of_thermodynamics

But time crystals aren't perpetual motion just by dint of not being closed systems at all, so they're kind of neither here nor there.