What does the morning in beginning of autumn mean?

This means that beginning of autumn came early.

Beginning of autumn has long been related to the time of beginning of autumn Day, that is, beginning of autumn time is in the morning, that is, from the early morning of beginning of autumn Day to noon on 12.

If you come to beginning of autumn after July of the lunar calendar, it is "late autumn". If it is still sultry in beginning of autumn and beginning of autumn in July of the lunar calendar, the sultry weather is called "autumn tiger".