The Dreyfus process was portrayed in the movie one one day. In real life the process went four days from the 19th-22nd December 1894. Furthermore the writing test happened on the second days of process while the sealed envelope with documents was given by Major Henry and Major du Paty on the third day.
The famous "open letter to the youth" by Emile Zola was released in December 1897, while in the movie he is seen quoting it in January 1898, after Esterhazy's release.