Time travel is no less realistic than most anything else accounting for magic in the mix. Just saying. But I know what you're getting at. Hence, why I hinted it would be a GM nightmare, and why games largely have rules against it. Don't worry, I'm doing something else. Just haven't decided what yet.
No even accounting for magic, it violates the laws of physics. Every other kind of magic could be accounted for by other real physical phenomena, even mental communication could just be a really well developed EM that talks directly to the brains of the recipient or reads the electrical signals of the recipient. Walking through walls could be as simple as a really unlikely quantum event that enough energy could in theory overcome. Time travel simply is impossible, as is manipulating time. It simply violates C or the energy requirements are simply too huge.
And our system easily handles time manipulation with the aforementioned infinity problems, which cause them to violate realism.
That's not to say that you can't have something move really fast, it's just that you can't use space-time as your base.
