The Feast of the Annunciation of the Blessed Virgin Mary does fall on March 25. There is some debate as to the origin of this feast and its date but it was certainly first celebrated sometime between 500-600 AD.
Christians in the early centuries (maybe around 200) are known to have recognized March 25 as the day of Christs crucifixion. The pseudo-Cyprianic work “De Pascha Computus”, c. 240 argues that the coming of Our Lord and His death must have coincided with the creation and fall of Adam, and since the world was created in the spring, the birth and death of Jesus must have also happened in the spring.
Since no historical documents are know to exist that verify any of these dates, it is all speculative at best and will likely never be known for certain.
At any rate, none of it has any bearing on the theology of the creation of Adam, the enunciation of Mary, or the birth or death of Christ. It is the truth of the lessons that are important, not the historical accuracy of the dates.