Now there was a man named Joseph, from the Jewish town of Arimathea. He was a member of the council, a good and righteous man, who had not consented to their decision and action; and he was looking for the kingdom of God. This man went to Pilate and asked for the body of Jesus. Then he took it down and wrapped it in a linen shroud and laid him in a tomb cut in stone, where no one had ever yet been laid. It was the day of Preparation, and the Sabbath was beginning. The women who had come with him from Galilee followed and saw the tomb and how his body was laid. Then they returned and prepared spices and ointments. On the Sabbath they rested according to the commandment. Luke 23:50-56 ESV
It was still Preparation Day according to Luke's passage.
Since it was the day of Preparation, and so that the bodies would not remain on the cross on the Sabbath (for that Sabbath was a high day), the Jews asked Pilate that their legs might be broken and that they might be taken away. After these things Joseph of Arimathea, who was a disciple of Jesus, but secretly for fear of the Jews, asked Pilate that he might take away the body of Jesus, and Pilate gave him permission. So he came and took away his body. Now in the place where he was crucified there was a garden, and in the garden a new tomb in which no one had yet been laid. So because of the Jewish day of Preparation, since the tomb was close at hand, they laid Jesus there. John 19:31, 38, 41-42 ESV
John gives more details that point to the same conclusion that Jesus was crucified and buried on the day of Preparation.
I take Mark to mean that the day of Preparation was ending and the Sabbath was approaching.