I would like to ask metaphysics that the first frost is destined to be 13 days after the vernal equinox and 12 days after the vernal equinox ... how did these first frost equinoxes come from?

Legislative rules are constantly revised according to the movement of celestial bodies. For example, in the dog days of the lunar calendar, there will be a ten-day difference compared with the difference before and after the end of beginning of autumn. If it ends before beginning of autumn, the middle dog will be added with ten days (* * * twenty days), and then the normal ten days will be counted. When the cycle lags behind the beginning of autumn, it will increase by ten days ... so it is called the lunar calendar. Its legislation originated from the creation branch of the emperor's study of the five elements. Emperor Yan's integration of crop cycle and other thoughts ... have some changes and modifications in the later period. It's really hard to say who invented it, but the source should be the astronomical calendar, the five elements branch, biological growth and other final products.