Time's Children

In this fantasy world there's Spanners, Walkers, and another group I can't remember. The first have the ability to travel great distances in a moment, the second can travel backwards in time, and then return, and the third can walk through walls but no one does that in this book. Tobias is a Walker, and is tasked with going back farther than anyone has. The catch is, he'll age those years he travels, too. There's also some demons – creatures with abilities of their own. But for such a fat book, not that much happens beyond a couple of fights, torture, and a lot of babysitting a royal baby. I stuck it out because, well, I'd got pretty far in and kept hoping it would improve. I won't be reading the concluding second part.