Jesus replied, “The Kingdom of God can’t be detected by visible signs. 21 You won’t be able to say, ‘Here it is!’ or ‘It’s over there!’ For the Kingdom of God is already among you.”
22 Then he said to his disciples, “The time is coming when you will long to see the day when the Son of Man returns, but you won’t sit. 23 People will tell you, ‘Look, there is the Son of Man,’ or ‘Here he is,’ but don’t go out and follow them. 24 For as the lightning flashes and lights up the sky from one end to the other, so it will be on the day when the Son of Man comes. 25 But first the Son of Man must suffer terribly and be rejected by this generation. (Luke 17:20-25 NLT)
Jesus makes it clear that the Kingdom of God and His return are two different things. God's kingdom is already among us. We are citizens in God's Kingdom through faith in Jesus Christ. Because we are sinful people living in a world darkened by sin, we may not always see or recognize God's kingdom among us.
Jesus will return. Here he warns about the things that will happen first and tells us not to fall for any false Messiahs. Jesus had to die and rise before He would return.
I think verse 22 is a warning about what would happen when the Romans destroyed the temple in 70 A.D. Jesus told people in other places to be prepared for that day.