How many days were the disciples in the upper room waiting for Christ?

In Matthew's Gospel, the disciples never met Jesus in the upper room - they went to a mountain in Galilee, where they saw Jesus.

In Luke's Gospel, Jesus met all the disciples in the upper room on the evening of the day of his resurrection and then took them out towards Bethany, where he was taken bodily up into heaven.

In John's Gospel, Jesus also met the disciples in the upper room on the evening of the day of his resurrection - but only ten of them, Thomas being absent. Jesus returned after eight days and met all the disciples. Later, he met them at the Sea of Galilee.

Mark's Gospel originally ended at verse 16:8, with the young man telling the women that Jesus was risen, and the fled in terror, telling no one. The 'Long Ending' (verses 19:9-20), added much later, has Jesus meeting the disciples as in Luke, but does not say when.