Josie's hair changes between black and auburn throughout the film. Particularly notable when she mistakes a student for John Barton at the train station. Her hair was colorful, turns black, then is colorful again in the next scene.
During the HSC scene, the board reveals that Josie is doing 2U ancient history, but the paper shown in the cut scene is a modern history paper.
Christina was conceived in 1945, so born no later than 1946. She had Josie when she was 17, meaning that Josie was born in early 1965 at the very latest (most likely earlier). Josie is 17 in the film, which would point to an early-1980s setting. However, several things--costumes, use of mobile phones, musical references, city features, various props and decor items--come from around the turn of the century, some 20 years later.