Jesus said that no man would know when the Kingdom would begin.
Daniel chapter 9 gives an outline of the timing of when the Messiah would show up on the earth and do his ministry and die.
If the Kingdom were to begin at the end of Christ's ministry, then Jesus wouldn't have said that the timing of the Kingdom rule beginning couldn't be calculated.
If Jesus was to receive the Kingdom as soon as he went to heaven, he wouldn't have told the apostles they had to wait, that it didn't belong to them to know.
That there was a second fulfillment of "tribulation" is apparent because Jesus never appeared in the heavens on the clouds and never sent his angels to gather Christians from all over the earth. Those things didn't happen in the first century because Jesus was telling what would happen in our day when he foretold those things.
There is a great tribulation coming on the earth. Christians who are asleep to it will be shocked. The religious institutions are about to be destroyed. Take refuge in God and Christ and endure in the faith and love and undeserved kindness of the Lord. Do not be afraid when the tribulation begins. It is for the appointed times. It has a beginning, and it will have an end. At the end of the 3 1/2 years, the UN and all human governments will be replaced with God's Kingdom. Keep the faith and wait for it with endurance. God has not abandoned us.
When you see the all the nations completely attacking religious institutions, you will know that Jesus took the throne in heaven. That will be the time to tell the world that the Kingdom has begun.
"As you go, preach, saying "Repent! The Kingdom of the heavens has drawn near."