What do you mean by eighteen days of the solstice?

It means that it is about to enter the dog days.

In a year, the days are the longest in spring, summer and summer. After the summer solstice, it takes about half a month, and the days gradually shorten. On the day of winter solstice, the days begin to get longer. There is a peasant proverb: the summer solstice is eighteen days, and the winter solstice returns on the same day.

When the weather is hottest, the temperature reaches its highest point. Folk say that there are eighteen days in summer solstice and the same day in winter, which is actually a method to calculate the dog days and cold days, and it is compiled into poems to deepen the impression and facilitate the calculation of dog days and cold days.