The Jewish clock time starts at 4 AM Roman time, our time according to the synchronization of John 19:14 with Mark 15:25. John was at the crucifixion site and could not mistake the clock time of the crucifixion. He reported the crucifixion time from a Roman time perspective.
Since Jesus declared around the time of Passover that there are 12 hours in the Jewish day, hence, the Jewish day ends at 4 PM. That is the correct conclusion from John 19:14 and Mark 15:25. The recorded times denote a discrepancy only for those who cannot understand. The evening starts at 4 PM and ends with sunset when darkness begins.
From the reported clock times of John 19:14 and of Mark 15:25, we deduce by tabulation that the evening clock hour which starts the Jewish day is set to 4 PM. Hence, the Jewish Sabbath starts and ends at 4 PM and not at sunset in the habitable part of the Globe.
Jesus answered, Are there not twelve hours in the day? If any man walk in the day, he stumbleth not, because he seeth the light of this world. John 11:9 KJV