So this question is based on something I heard that might be incorrect. I heard that in Canon Law which deals with certain days, unless the specific law states otherwise, the day begins at local midnight.
Why would Catholic law treat days in this way, seeing as by the Jewish reckoning, a new day begins at sundown, which is based on the wording of Genesis, which both religions share?
I am also pretty sure that some holy days use the old reckoning (I think things like lent end at sundown on Good Friday or something similar?). So seeing as most, or at least many of the first Christians were Jews, at what point did the church change from considering days to begin at sundown, and say that days now begin at some arbitrary point in the middle of the night?