What does Luke 24:50 mean?

It is forty days since Passover and Jesus' death; ten days to Pentecost and the arrival of the Holy Spirit (Acts 1:3). Jesus has visited enough of His disciples that the witness of His resurrection is irrefutable by reasonable people (John 21; 1 Corinthians 15:5–7). Jesus has shown His followers how He fulfilled Scripture (Luke 24:45–48) and has spoken about the kingdom of God (Acts 1:3).

At this late time, the disciples are still confused about what the kingdom of God is. They ask Him, "Lord, will you at this time restore the kingdom to Israel?" (Acts 1:6). That would be nice. But the Jewish leadership has not repented. They have not led the people to their Messiah. It doesn't appear the core group has even gone out to validate the rumors they must be hearing from those who have seen Jesus.

Part of the covenant the Israelites made with God addresses reconciliation after a long period of rebellion:

But if they confess their iniquity and the iniquity of their fathers in their treachery that they committed against me, and also in walking contrary to me, so that I walked contrary to them and brought them into the land of their enemies—if then their uncircumcised heart is humbled and they make amends for their iniquity, then I will remember my covenant with Jacob, and I will remember my covenant with Isaac and my covenant with Abraham, and I will remember the land." (Leviticus 26:40–42)

The leaders refuse to do this. They will not be reconciled until the end times. Jesus explains that knowing when this will happen is not the disciples' business. Their business is to receive the Holy Spirit and be His "witnesses in Jerusalem and in all Judea and Samaria, and to the end of the earth" (Acts 1:7–8).

Their obedience is what eventually led to you reading this now.