The Post War Automobile period is not clearly defined, but nostalgic folks think of cars of the fifties as post war ( WW II ) automobiles. New models started to appear in 1949. Most of the automobiles produced immediately after the war were the same as the military models produced during the war and in 1940 - 1942. So the post war car era didn't begin on a specific date, but about 1948, give or take a year or two.
Looking through the literature on old cars, the Post War era does not have a clear end, but rather faded into the past over a span of time from 1958 to 1963. The introduction of the compact car about 1960 and major body restyles by all manufacturers in 1960, 1961, and 1962 seems to indicate the start of a new era in the automotive calendar.
Bob Neville in his book " Real Steel" treats the period 1958 to 1960 as a transitional time where the manufacturers went to extremes with fins, chrome and largeness to capture declining sales at the end of the post-war period. The Edsel is a good example of the attempt to bolster sales. The increasing market share ( up to 10% by 1960 ) captured by Volkswagon and other small foreign cars also influenced the start of a new era. The declining sales at the end of the fifties also meant the end of marks such as Nash, Studebaker, Packard and others, and again the end of the Post-War era.
The American Car Spotter's Guide for the period 1940 to 1965 shows the significant changes in body styles over the years. The cars of the fifties are distinctive from the pre-war automobiles. The automobiles produced after 1962 are distinctive from the cars of the fifties. The compact cars introduced a whole series of new names to the buying public. Nova, Falcon, and Dart are but a few of the models that did not exist in the post-war era. In body style, engineering and name it appears that the last true post-war automobile was the 1961 Desoto.