First off, he's right, he and I did talk about this at length. Secondly, he's had this idea since before the Templars and since before we classified existence. I very well think we can work with him to fix the holes and patches, that's our duty as staff is to help the members. That said, Nisorin is mistaken, his character travels outside the Dimensional Plane on a regular basis, not existence. But I don't think leaving existence, or leaving the dimensional plane, is an explanation for the time travel.
As for why you're character can travel through time though, a better explanation would be that the dark void is an anomaly in time itself (only not nearly as extensive), sort of like a copy of the Records of Time, in that it's connected to various parts of the timeline. Which actually makes quite the exciting plot twist.