The movie is set around 1905, as can be seen from the "contract" that Gustav Adolf gave Maj early in the movie, but Edvard tells Emilie that he heard that the universe is expanding. Slipher discovered the red shifts in some nebulae/galaxies in 1912, an observation that suggests that these objects are moving away from us; Hubble's law of the expanding universe was published in 1929; and the big bang theory become popular in the 1950s.
Among the Christmas decorations in the Ekdahl house, there is a garland of miniature flags of Scandinavian countries, including the Finnish flag. The Finnish flag was in fact only designed and adopted after Finnish independence in 1917, a decade after the events of the film.
In one scene, Gun Wållgren refers to the historically famous Belgian town of Waterloo, and uses an English pronunciation, which is an obvious modern trait - probably as a result of the popularity of the eponymous song from the pop group ABBA.
The movie opens at Christmas 1907. The bishop's proposal to Emilie could not have been any earlier than mid-1908, which means that the end of the film could not have taken place any earlier than mid-1909. Emilie refers to _A Dream Play_ as a "new" play by Strindberg, but the play had already had its Stockholm premiere in 1907, i.e. prior to the start of the action of the film.
In the theatre scene, early in the movie, Georg Årlin, who plays a high ranking military man, is seen whispering with a person sitting next to him. The next shot shows other people talking, and then Årlin is seen behind them at the left corner, in conversation with no one, staring into space in front of him.