When will it cool in early autumn and how long will it cool in beginning of autumn?

It will be cool after beginning of autumn 15-2.

After beginning of autumn, the hot weather may not subside until the summer heat or the Millennium. After beginning of autumn,15th day is the summer solar term, which means the end of high temperature in summer. Generally, the temperature will gradually decrease at this time.

If you encounter autumn tiger weather, you have to wait until the Millennium solar term, that is, the temperature drops. At this time, there will be basically no continuous high temperature weather.