Mk.15:25: “Now it was the 3rd hour and they crucified him.”
John 19:14: “It was about the 6th hour he was on trial.”
Mark used the Jewish time frame.
3rd hour of the day they crucified him.
Day starts at sun up.
About 9am
John used the Roman time frame.
6th hour of the day he was on trial.
Day starts at 12 midnight
6am in the morning
The trial started at 6am in the morning.
3 hours later Jesus was crucified at 9am
It ended at 3pm.
John 18
28. Then led they Jesus from Caiaphas unto the hall of judgment: and it was early morning; and they themselves went not into the judgment hall, lest they should be defiled; but that they might eat the passover.
early morning refers to the fourth Roman watch, which was 3 a.m. to 6 a.m.