I keep forgetting Vint himself doesn’t know Diana had been time traveling until like. The end of season two at least. I don’t think he’d know she rigged the pocket watch either…
Perhaps that’s the big case Vint thinks he’s trying to solve in season 2 when he gets sent back (before Diana disappears). The time traveler and/or the person who put him through this.
(Though it’s distinctively NOT the person who built the watch… this happens to be a red herring in the series itself!)
Maybe in season 1 he gets tipped off that the time traveler is from his original time period with an item from another time… possibly something Diana planted herself???
(I adore the idea that Diana is placing clues in certain times/places knowing Vint would connect the dots one way or another… he’s the detective after all!!!)