The film's opening shows a Polish city [later revealed to be Krakow] in the midst of heavy fighting. Krakow was abandoned by the Germans and taken by the Red Army with no destruction or street fighting.
Robert and Frieda visit a cinema that is showing Gaumont's newsreel film of Auschwitz, which would have been shown in cinemas in early April 1945. However, the implication from the time-line of the film is that it's late summer or early autumn, since it's portrayed as after the 1945 General Election, which took place in July.