Excuse me, is December based on the first day of the first lunar month and the first day of the second lunar month?

Don't! December construction is: build Yin in the first month, Mao in February, Chen in March, Si in April, Wu in May, Wei in June, Shen in July, You in August, Hai in September, Zi in November and Chou in December (meaning "build" in December of the first month and "Yin" in the ground). Of course, this is all based on the 24 solar terms-beginning of spring is the first month. Long summer is the beginning of April, awn seed is the beginning of May, and summer is the beginning of June. Take beginning of autumn as the beginning of July, the Millennium as the beginning of August and the cold dew as the beginning of September; Take beginning of winter as the beginning of October, heavy snow as the beginning of November and slight cold as the beginning of December.

Also, even if the first day of the first month really catches up with the "Jianzi" (built in December, the main branch is "Zi"), it will not be "ugly" until the first day of February. In other words, if the first day of the first month catches up with "Jian" and "Zi", then the first day of February will not catch up with "Jian" or "Ugliness".