Before the Coffee Gets Cold, by Toshikazu Kawaguchi

At a very special coffee shop in Japan, you can time-travel into the past, as long as you sit in a particular chair and don't move from it, and only for as long as it takes for your coffee to go cold. You can't change the past, you can only travel within the cafe (so anyone you want to visit in the past must have also visited the cafe), and a ghost is already in that chair so you have to wait till she gets up to go to the bathroom.

This book sounded very charming, but I got off on a bad foot with it because it took FOREVER to explain the rules before anyone traveled. When I learned that it originated as a stage play, that made more sense - the back-and-forth about the rules was probably very funny with good actors. In book form, it was interminable.

The vignettes are touching, but in a manufactured tearjerking way, like the woman who will die if she gets pregnant so of course she decides to keep her pregnancy so her baby will have a chance at life or the woman whose sister storms out angrily after a fight and immediately gets killed in a car crash. I was expecting Banana Yoshimoto and I got Jodi Picoult.

Maybe later books in the series are better, or at least don't spend so long explaining the rules.