In the scene when Andy first comes to Shawshank, Red said that it was 1949. After a while, the Sisters start to beat Andy up, and Red said that he thought the first 2 years were the hardest for Andy. They show a short shot of Andy walking around in the snow, commonly meaning (especially in Maine) that it was wintertime. Later on when Red first talks about the resurfacing project for the plate factory roof, he said that it was spring 1949.