I don't think he'll be able to. I remember I used to time slip (it lasted a few seconds only for me) and I tried to keep something, anything, to prove to my parents I wasn't imagining. Got an old cup, just to slip on the wet floor and fall, breaking the thing; got a piece of paper, it flew from my hands into a river; the worst was when I got a whole book, and somebody robbed me...

I think time have a way to avoid these kinds of paradox on itself...