Besides Luke 4:17-21 which was already mentioned, where Jesus quotes from Isaiah 61:1-2, the Bible does refer to the "gap" in other places.
Hosea 3:4 For the sons of Israel will remain for many days without king or prince, without sacrifice or sacred pillar and without ephod or household idols.
Hosea 3:5 Afterward the sons of Israel will return and seek the LORD their God and David their king; and they will come trembling to the LORD and to His goodness in the last days.
Israel would not have a king again until the Messiah's kingdom, but it was unknown how long that might be, just "for many days."
Luke 19:11 While they were listening to these things, Jesus went on to tell a parable, because He was near Jerusalem, and they supposed that the kingdom of God was going to appear immediately.
Luke 19:12 So He said, "A nobleman went to a distant country to receive a kingdom for himself, and then return.
Luke 19:13 "And he called ten of his slaves, and gave them ten minas and said to them, 'Do business with this until I come back.'
Luke 19:14 "But his citizens hated him and sent a delegation after him, saying, 'We do not want this man to reign over us.'
Luke 19:15 "When he returned, after receiving the kingdom, he ordered that these slaves, to whom he had given the money, be called to him so that he might know what business they had done.
Jesus gives a parable about the kingdom and when it will appear. A nobleman (Christ) went to a distant country (earth) to receive a kingdom; He doesn't receive it at that time--He would return. He gives instructions while in this distant country and tells the people He will come back--He doesn't say how long that will be. Some time passes, and no one knows for sure just when He is coming back. But He eventually returns and receives His kingdom, at which time His faithful servants are rewarded with responsibilities in the kingdom.
John 14:3 "If I go and prepare a place for you, I will come again and receive you to Myself, that where I am, there you may be also.
Jesus doesn't say how much time will pass between His leaving and the rapture, just that He is leaving, but that He will come again and take us away with Him. But after the resurrection, the disciples ask, isn't it time for the kingdom yet?
Acts 1:6 So when they had come together, they were asking Him, saying, "Lord, is it at this time You are restoring the kingdom to Israel?"
Acts 1:7 He said to them, "It is not for you to know times or epochs which the Father has fixed by His own authority;
Jesus gives them no time clues as to when the kingdom will appear, then ascends back to heaven, for an indefinite period of time. God gave definite time periods when dealing with Israel, but not regarding the church age: “for many days.”