It seems appropriate to fill in some of the remaining blanks in the story of Jesus, even though it requires us to look beyond the gospels somewhat and into the rest of the New Testament. Both Luke and Acts tells us that Jesus ascended to heaven from the vicinity of Jerusalem. Luke 24:51 says he was taken into heaven, meaning into the skies. Acts 1:9 says that, after he was taken up, a cloud hid him from the eyes of the disciples. Christians refer to this as Jesus' ascension, and many Christian traditions celebrate "Ascension Day" on a Thursday, forty days after Easter.
Based on Psalm 110:1, Christians also speak of the "session" or seating of Jesus on the right side of God's throne: "The Lord said to my Lord: 'Sit at my right hand until I make your enemies a footstool for your feet'" (Acts 2:34-35). This verse was probably very important indeed for the earliest Christians as they tried to make sense of Jesus' death and resurrection. Mark 12:35-37 remembers Jesus himself mentioning this verse in his debates with certain teachers of the law.
The key is that the earliest Christians saw Jesus' sitting at God's right hand as his enthronement as cosmic king. Acts 2:32-33 tell about how "God has raised this Jesus to life, and we are all witnesses of it. Exalted to the right hand of God, he has received from the Father the promised Holy Spirit and has poured out what you now see and hear." Acts then quotes Psalm 110:1, making it clear that David did not ascend to heaven--in other words the words are surely about Jesus sitting at God's right hand. Peter's sermon then comes to this conclusion: "Therefore let all Israel be assured of this: God has made this Jesus, whom you crucified, both Lord and Messiah" (2:36).
The timing of Jesus becoming Lord and Messiah, royal titles, is thus when Jesus sat at God's right hand, after rising from the dead. He was the "heir apparent" before that time, but fully took on the role as king, as "anointed one," "Messiah," after he rose from the dead. And a number of passages make it clear that Jesus fully took on the title "Lord" at his resurrection. "Therefore God exalted him to the highest place and gave him the name that is above every name, that... every tongue acknowledge that Jesus Christ is Lord" (Phil. 2:9-11). Similarly Romans 10:9: If you declare with your mouth, “Jesus is Lord,” and believe in your heart that God raised him from the dead, you will be saved." To declare Jesus as Lord implies that you believe God raised him from the dead.
"Son of God" is another royal title Jesus fully took on at that point.  Romans 1:3 says that Jesus was "appointed Son of God in power by his resurrection from the dead." Acts 13:32-33 again places Jesus' assumption of this title at the point of his resurrection: "What God promised our ancestors he has fulfilled for us, their children, by raising up Jesus. As it is written in the second Psalm: "You are my son; today I have become your father.'"
What is Jesus doing now in heaven as he sits at God's right hand? ...
 The phrase "Son of God" is yet another case study in how words and phrases can take on different meanings and connotations in different contexts. In the context of Acts and Paul, the phrase "Son of God" seems to be a royal title that a king assumes upon his ascension to the throne. In a sense, a king of the Ancient Near East was not Son of God one moment and then became "Son of God" the next moment as he became king. Thus Psalm 2 is often considered an "enthronement psalm" in its original Old Testament context.
However, as Christians we also believe that Jesus was "eternally begotten of the Father" and thus that he was always the Son of God in terms of his being, not only his office. Scholars like Richard Bauckham have argued that the New Testament already starts to have this sense in passages like Hebrews 1:5 (e.g., ***). Others like James Dunn have argued that in Acts, Paul, and Hebrews, the title is still a matter of Jesus' office as king (e.g., Christology in the Making).
We do not have to pick one or the other option when it comes to the question of truth. As Christians we both believe that Jesus was always the Son of God and that Jesus assumed the role of king of the cosmos more powerfully after he rose from the dead.