I mean look at the clock. Now look again. Time has moved forward with you!
Okay, okay... What he is saying is that if you're on something that travels 98% the speed of light, time will pass slower. As Einstein theorized “as objects accelerate through space, the rate at which time passes for them slows down”. So a day on board the something would be equal to a year on Earth which will push them forward in time.
He goes onto say that travelling backwards in time is RIGHT OUT! Which is a good thing because of all the mess it could cause stopping new Time Travelers from going back and stopping Hitler...
As a Science Fiction junkie I always enjoy time travel speculation. My favorite essay on the subject was by Larry Niven: "The Theory and Practice of Time Travel" that appears in All the Myriad Ways.
This essay looks at the implications of time travel, particularly at the grandfather paradox:
"NIVEN'S LAW: IF THE UNIVERSE OF DISCOURSE PERMITS THE POSSIBILITY OF TIME TRAVEL AND OF CHANGING THE PAST, THEN NO TIME MACHINE WILL BE INVENTED IN THAT UNIVERSE." Thus all possible time paradoxes are evaded.
He further challenges conceptions of time travel: "If time travel is so manifestly impossible, why does every good and bad science fiction writer want to write a new, fresh time travel story?"
My favorite TV series, Doctor Who. Is all about time travel and it avoids most of the pitfalls by just never delving into the paradox other then saying it is a paradox and just go with the flow.
Suspension of disbelief is a powerful thing.