It is definitely one of my favourite #TimeTravel movies
It being contained in a small location keeps it enjoyable and stops it getting too messy. And I think this is partly because it's a Japanese film.
If it was made in the West, I imagine it going into something much bigger, somehow leaking out from the location, with the film makers probably trying to make some deep, mind-bending loop ending.
This movie is entirely unpretentious but very, very clever.