Why can the time of solar terms such as long summer be accurate to what time?

Ancient working people divided a year into 24 equal parts according to the natural phenomena such as the position of the sun and the moon, the weather and the growth of animals and plants at the beginning of the month and in the middle of the month. At present, the 24 solar terms are divided according to the position of the sun on the ecliptic, and every 15 degrees forward from the vernal equinox is regarded as a solar term. In ancient times, the period from winter solstice to summer solstice and then to winter solstice (about 365.25 days), that is, the year of the Tropic of Cancer, was usually divided into 24 segments (each segment was about 15: 05), and each segment started with a solar term, namely, winter solstice, slight cold, severe cold, beginning of spring, rain, fright and vernal equinox.