This book is a delight.

Finn Einstein (Reform, loving parents, good at school, zero friends) and Ezra Rosen (Orthodox, middle child problems, doesn't try in school, many friends) are celebrating their bar mitzvahs right next to each other at the same New Jersey hotel. Finn realizes they are stuck in the same time loop, and together they try to break out of it, relying on Finn's knowledge of time loops in movies, and with help from Ezra's new rabbi and a physicist at the physicist convention also taking place at the hotel that weekend.

Yes, the names Einstein and Rosen are deliberate.

The author is having so much fun here. There are so many great lines. When the rabbi is offering to help them, he says "come with me if you want to learn".

The plotting and the characterization are spectacular, there's so much fun show vs tell that the author is relying on you putting the pieces together. For instance, Finn refers to his parents as helicopter parents, but they are not shown that way at all; in fact, they're so permissive that something has to be wrong. Oh no, thought I, putting some details together, if this is the novels of my childhood, Finn has cancer and is about to die, or his parents have cancer and is about to die. But this is a midgrade humor novel! That would be too depressing! Instead, his mother has stage two thyroid cancer that is depicted as being very treatable, they just don't want to tell him until after his bar mitzvah.

And Ezra? His family's big tension that's causing so many fights? Ah, well, property taxes are going up, they can't afford to live here anymore (Ezra's bar mitzvah is being funded by the community and his Uncle Chaim), so they're moving to a different town. They just didn't want to tell him until after his bar mitzvah that they're moving literally that week because they already sold the house. But it's all going to be fine! His dad will find another job, and his sister Avital's big secret is that she has a job at the local pizza place that she doesn't want anyone to know about because her parents want her to focus on school in her senior year. Even better, now they'll be in the same town as Finn, within walking distance!

They've all learned an important lesson about appreciating every day you have with the people you love, and also gained a good friend. And robbed a bank. And won the lottery. And realized that there are some things, no matter how many time loops you try it in, that you just can't change.

(Yes, it's extremely preslashy.)