While Jesus “came as a thief” to his enemies, it was not like that for his disciples.
First, the apostle Paul said: “But concerning the times and the seasons, brethren, you have no need that I should write to you. For you yourselves know perfectly that the day of the Lord so comes as a thief in the night. For when they [Jesus’s enemies] say, ‘Peace and safety!’ then sudden destruction comes upon them, as labor pains upon a pregnant woman. And they shall not escape. But you, brethren, are not in darkness, so that this Day [second coming] should overtake you as a thief. You are all sons of light and sons of the day. We are not of the night nor of darkness” (1 Thess. 5:1–4, italics mine).
As the passage says, Jesus’s disciples were “not in darkness, so that this Day should overtake [them] as a thief” (v. 4). The timing of the second coming would not be a surprise to the disciples in the least. After all, Jesus had specifically told them approximately twenty years earlier (in AD 30) that he would come within a generation (Matt. 16:28, 10:23, 24:30–34, 26:64). So while they did not know the exact day and hour, they certainly knew the approximate time frame.
In fact, Jesus had even told his disciples (in AD 30) the various precursors to watch for, such as false messiahs, wars and rumors of war, persecution, the abomination of desolation, and the tribulation (Matt. 24:4–28). “And immediately after the tribulation of those days the sun will be darkened, and the moon will not give its light; the stars will fall from heaven, and the powers of the heavens will be shaken. Then the sign of the Son of Man will appear in heaven, and then all the tribes of the earth will mourn, and they will see the Son of Man coming on the clouds of heaven with power and great glory” (vv. 29–30, italics mine).
And when did Jesus say this would happen? “Assuredly, I say to you, this generation will by no means pass away till all these things take place” (v. 34).
Clearly, the disciples were not in the dark regarding the timing of the second coming.
Second, Jesus discussed his “thief coming” in Revelation too (through an angel): “Behold, I am coming as a thief” (Rev. 16:15). And what was the reason for this thief coming? To avenge the blood of the saints and prophets: “For they [Jesus’s enemies] have shed the blood of the saints and prophets” (Rev. 16:6). And when would this thief coming/judgment happen? “[These things] must shortly take place. ‘Behold, I am coming quickly! Blessed is he who keeps the words of the prophecy of this book…for the time is at hand’” (Rev. 22:6–10).
This must have happened soon after Revelation was written.
Jesus had also warned about this same judgment during his earthly ministry (in AD 30). As you read the following passage, notice the reference–just like in Revelation–to the blood of the prophets:
“Therefore you [scribes and Pharisees] are witnesses against yourselves that you are sons of those who murdered the prophets. Fill up, then, the measure of your fathers’ guilt…Therefore, indeed, I send you prophets, wise men, and scribes: some of them you will kill and crucify, and some of them you will scourge in your synagogues and persecute from city to city, that on you may come all the righteous blood shed on the earth, from the blood of righteous Abel to the blood of Zechariah, son of Berechiah, whom you murdered between the temple and the altar” (Matt. 23:31–35).
Just like in Revelation, Jesus talks about avenging the blood of the saints/prophets. And when did Jesus say this would happen? He tells us in the very next verse: “Assuredly, I say to you, all these things will come upon this generation” (v. 36).
The timing of the second coming was not a surprise for Jesus’s disciples.