When did Hefei fall?

Mid-late September. Traditionally, "beginning of autumn" in 24 solar terms is regarded as beginning of autumn, but beginning of autumn does not mean the end of extremely hot weather. "Autumn" is defined according to the standard of dividing four seasons in climatology. Only when the average daily temperature is stable below 22℃ for five consecutive days can it really enter autumn. The weather in Hefei starts to get cold in September every year, so it usually starts in the middle and late September.