Christina was conceived in 1945, so born no later than 1946. She had Josie when she was seventeen years old, meaning Josie was born in early 1965 at the very latest (most likely earlier). Josie is seventeen in the film, which would point to a setting around 1980 (give or take). 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 twenty years later.
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 colored, turns black and is then colored again in the next scene.