At the time of the film's production, SS-Oberführer Dr Gerhard Klopfer was the only living attendee of the Wannsee Conference. He died on January 29, 1987 at the age of 81.
Most of the conversations at the beginning of the film, in particular the small talk between offices, the dialogue between the SS and the secretaries, and the emergency phone call regarding a transport of Jews in the east, is entirely dramatic license. The actual minutes for the conference begin after Heydrich convened the meeting - exactly what the Nazi officers were doing before Heydrich arrived is not historically known and is dependent on second hand testimony and speculation.
The film takes place on January 20, 1942.