Jesus Christ does not lie. He told the hypocrites they would receive no sign save the sign of Jonah. As Jonah was in the belly of the fish three days and three nights so the Son of Man would be in the belly of the earth three days and three nights. The first day does not matter. Days venerated do not matter, but the attitude of the heart soul and mind do matter in the sight of God.
Personally, I cannot say I know with certitude which day He, our Salvation, was crucified, but He was crucified for my sins and the sins of all who come to Him in Spirit and Truth. He fulfilled all the law and Moses; why not begin with that? I did, and so did many others. It is the easies solution, that is, if it does not sound too "Jewish" for some.