But if time travel is a thing, imagine the whole new time nightmares! Oh you went back a year with your phone? Now all your TLS root certs are invalid because you're before the start date. Or you have files/emails/whatever that are dated in the future. I guess you can get to that state by just setting your clock forward but I imagine some stuff would break.
I worked on a project that had a few spots where we compare a saved timestamp to the current time. During testing, the client would randomly change their device time a few days forward or backward and complain that things weren't working as expected. I had to explain to them multiple times that they were basically time traveling, and the program was actually handling it fairly well all things considered.