Mark tells us that Jesus was crucified at the third hour. But skeptics claim there is a contradiction because John says it was at least three hours later, since at “about the sixth hour” Jesus was still with Pilate before the Jewish crowd (John 19:14). Matthew (27:45) and Luke (23:44) also have Jesus already on the cross at the sixth hour, so they, too, appear to contradict John’s account.
So what time of day was Jesus crucified? This has a very simple explanation. Matthew, Mark, and Luke used the Jewish system of keeping the time, where the day was reckoned as starting at 6 a.m. (sunrise). John, on the other hand, used the Roman system, which (like our time) counts the day as starting at midnight. In both cases, Jesus was crucified at 9 a.m.
Mark 15:25 Now it was the third hour, and they crucified Him.