My pick would have to be the A Whole Nother Story trilogy, in which (spoiler warning) you can only travel back in time. But because time is in a loop of sorts, if you go before the beginning of time, you will be at the end of time. From there you can go back to any time you want to. And time paradoxes cannot be produced. Plus, your memories from the previous timeline exist as well as the memories from the new one.
Hold up, there was TIME TRAVEL in that?? Frick, there are downsides to reading books when you are way too young to be reading them… Guess it will have to go on the “must re-read this as an adult” list!
Yeah, the war story is told chronologically but he keeps jumping around to different points in his life. There a long (and cool) but about how the aliens who take him see all of time at once and live in all of it simultaneously (they are responsible for the end of the universe too). They say our point of view is like being strapped onto a train car, traveling parallel to some mountains with a metal case around our head and our very long, narrow tube coming out of it that we can see down. Our view of time is extremely limited and narrow, and only progresses in one direction.
The book says something about being “unstuck in time”. I interpret that as the main character has severe PTSD and uncontrollable flashbacks. Other people interpret it as time travel.