In Jewish culture the eight days from birth to circumcision always counted the day of the birth. For example, if a child was born on a Wednesday then he would be circumcised the following Wednesday.
Keep in mind that Jewish days begin at sunset and that Jesus was born in the evening. For example, if Jesus was born on what we consider Wednesday evening, in Jewish culture that is actually the start of Thursday. In this case Jesus would have been baptized the following Thursday during the day. All Jewish circumcisions happen during the day.
We celebrate Mary on the first day of the year because she is the pinnacle of creation, the door through which salvation came to mankind. The fact that Jesus was circumcised on the same day is not relevant. We celebrate Jesus baptism instead.
Jesus’ birth through the beginning of his ministry - the hidden years of his life - are condensed in the Church calendar as follows:
Dec 25 - Nativity of the Lord
Dec 27 - Holy Family
Dec 28 - Holy Innocents: the first to die for Jesus
Dec 1 - Mary, Mother of God
Jan 3 - Epiphany of the Lord
Jan 10 - Baptism of the Lord: the start of Jesus public ministry