The book of John and the first three (synoptic) gospels may have some differences among them, but few seem contradictory. In his exhaustive book, “The Historical Reliability of the Gospels“, Craig Blomberg notes that perhaps the most puzzling difference is in Mark 15:25 and John 19:14 regarding the hour of Jesus’ crucifixion. Mark said that Jesus was crucified at ‘the third hour’ or in some translations, nine in the morning; whereas John said that Jesus was crucified at ‘the sixth hour’ or noon, according to translation.
Blomberg writes that it is plausible that Mark was using a common reference for that era, which split the time of day into quarters, so to say ‘the third hour’ could mean anytime between nine and noon. John’s use of ‘the sixth hour’ would have been a more precise measurement of time since the day began at 6 a.m. So the sixth hour would have meant about noon as well.
For Mark to talk in approximate hours makes sense, considering the world did not revolve as much around precise timekeeping then; and still today, Western missionaries have to exercise a lot of patience and flexibility in some countries. Agreeing to meet at a certain time of day could mean waiting for hours.