The timing of the ascension
Luke ends his gospel with the ascension on resurrection day; Acts, by the same author, places it forty days later.
Luke 24:50-53
50He led them out as far as Bethany, and he lifted up his hands, and blessed them.
51While he blessed them, he withdrew from them, and was carried up into heaven.
52They worshiped him, and returned to Jerusalem with great joy,
53and were continually in the temple, praising and blessing God. Amen.
Acts 1:3-11
3To these he also showed himself alive after he suffered, by many proofs, appearing to them over a period of forty days, and speaking about God’s Kingdom.
4Being assembled together with them, he commanded them, “Don’t depart from Jerusalem, but wait for the promise of the Father, which you heard from me.
5For John indeed baptized in water, but you will be baptized in the Holy Spirit not many days from now.”
6Therefore when they had come together, they asked him, “Lord, are you now restoring the kingdom to Israel?”
7He said to them, “It isn’t for you to know times or seasons which the Father has set within his own authority.
8But you will receive power when the Holy Spirit has come upon you. You will be witnesses to me in Jerusalem, in all Judea and Samaria, and to the uttermost parts of the earth.”
9When he had said these things, as they were looking, he was taken up, and a cloud received him out of their sight.
10While they were looking steadfastly into the sky as he went, behold, two men stood by them in white clothing,
11who also said, “You men of Galilee, why do you stand looking into the sky? This Jesus, who was received up from you into the sky, will come back in the same way as you saw him going into the sky.”
What each tradition says
Rabbinic / Midrashic
No sourced position found. Checked: The Jewish Encyclopedia (1901-1906) s.v. 'Ascension' (treats merkabah/mystical ascent, Moses/Elijah/Enoch — no Jesus, no New Testament); s.v. 'Jesus of Nazareth' full text searched for 'ascension'/'ascended' (only the empty-tomb claim and the Toledot legend, nothing on the Luke 24 / Acts 1 timing); s.v. 'Christianity in its Relation to Judaism' (no 'ascension' at all); no Jewish source commenting on the Lukan/Acts ascension chronology was found.
Patristic
Augustine says Luke appends the statement of the ascension just as if it followed immediately upon the Lord's words. He places it at the same time as the other transactions on the first day of the week, the day on which the Lord rose again.
Augustine of Hippo (354-430), The Harmony of the Gospels (trans. S. D. F. Salmond), in NPNF ser. 1, vol. 6 (ed. Philip Schaff; T&T Clark, Edinburgh, 1888) — Book III, ch. 25 ('Of Christ's Subsequent Manifestations of Himself to the Disciples')
Catholic
Aquinas says that while a heavenly place was fitting for Christ after rising to immortal life, he delayed his Ascension to confirm the truth of his Resurrection. It is written in Acts 1:3 that he showed himself alive after his Passion by many proofs for forty days, appearing to them.
Thomas Aquinas (1225-1274); trans. Fathers of the English Dominican Province (1920), Summa Theologiae, Second and Revised Edition (New Advent) — III, q.57, a.1 ('Whether it was fitting for Christ to ascend into heaven?'), reply to objection 4
Orthodox
Chrysostom says that during the forty days Jesus was not always with them as before the Resurrection. The writer says “during forty days,” not “forty days”: Jesus came and disappeared again. This led them to higher conceptions, so they would believe the Resurrection and understand Him as greater than man.
John Chrysostom (c. 349-407), Homilies on the Acts of the Apostles, in NPNF ser. 1, vol. 11 (ed. Philip Schaff; T&T Clark, Edinburgh, 1889) — Homily I (on Acts i. 1-2), on verse 3 ('being seen of them during forty days')
Reformed / Protestant
Matthew Henry says he was seen by them for forty days, not living constantly with them but appearing frequently. These appearances gradually brought them to full satisfaction, so that all their sorrow over his departure was removed.
Matthew Henry (1662-1714), Commentary on the Whole Bible, vol. 6: Acts to Revelation (1706-1721) — Exposition of Acts 1:3
Evangelical
Wesley notes that Acts 1:3 summarizes in general what Christ said to the apostles during the forty days, while Acts 1:4 and following declare what he said on the day of his ascension. Luke had brought his former account down to that day, and Acts begins from that day.
John Wesley (1703-1791), Explanatory Notes upon the New Testament (1755; CCEL's 'Wesley's Notes on the Bible') — Notes on Acts 1:1-2 (verse 2, 'until the day in which he was taken up')