This Bible contradiction is from the Skeptic's Annotated Bible.
At the third hour
Mark 15:25 View context
And it was the third hour, and they crucified him.
Sometime after the sixth hour
John 19:14-16 View context
And it was the preparation of the passover, and about the sixth hour: and he saith unto the Jews, Behold your King!
But they cried out, Away with [him], away with [him], crucify him. Pilate saith unto them, Shall I crucify your King? The chief priests answered, We have no king but Caesar.
Then delivered he him therefore unto them to be crucified. And they took Jesus, and led [him] away.