What does 99 mean?

"99 Days" is a folk method for calculating the flowering dates of cold weather and warm spring in China.

"99 days", commonly known as the number nine, is a folk method to calculate the date of cold weather and warm spring in bloom. Generally, March and April are the coldest time, which is the coldest time of the year. When you count to nine "nine days" (998 1 day), spring will be deep and warm, and everything will be full of vitality. This is the time for spring ploughing.