User blog comment:Neko Neko no Mi Model: Russian Blue/The potential merits of a Time-Time fruit, particularly one held by an Admiral/@comment-25400375-20180527105216

Well, I’ve seen some interesting time travel fanfiction stories featuring the concept for One Piece and otherwise, but since it “could” be a Devil Fruit power, it’s best to give it some limitations, like a Time Human can’t mentally travel back to a time from before they ate it. I say that because Oda clearly stated at some point that two Devil Fruits of the same nature can’t exist at the same time, or something like that. Therefore, it would be counterproductive if a whole being was sent back in time. Now that I think about it, though, it could be best to save time travel itself for an Awakened Devil Fruit.

I guess other abilities would be slowing time down to a degree and opening a window to the past as long as you know the exact time and place you’re looking for, but making up original Devil Fruits isn’t exactly my forte, so you know.