when does rogue one take place

The movie Rogue One: A Star Wars Story takes place just before the original Star Wars film (Episode IV: A New Hope). Specifically, most of Rogue One's story happens in 1 BBY (Before the Battle of Yavin) and it ends shortly before the events of A New Hope, which is set in 0 BBY. This means Rogue One is set about one week before the events of A New Hope as it details the mission to steal the Death Star plans, an event referenced in the opening crawl of A New Hope.