The manner of his ascension was such that it would qualify the apostles to serve as witnesses of that fact, even as they were of Jesus’ resurrection. (Ac 1:3)

Since Acts 1:3-9 shows that Jesus’ ascension took place 40 days from the time of his resurrection, there is a time lapse between the events recorded at Luke 24:1-49 as occurring on Jesus’ resurrection day and the ascension of Jesus as described in verse 51 of that chapter.