There are a number of places in the Bible, other than Matthew, Mark, and Luke, where God tells us that we will not know the time of His coming, but most refer to the Day of the Lord which comes at the very end. For example there is 2 Peter 3:10-- "But the Day of the Lord will come like a thief. The heavens will disappear with a roar, the elements will be destroyed by fire, and the earth and its works will be laid bare."
And there is 1 Thessalonians
5:1-2-- "Now about the times and seasons, brothers, we do not need to write to you. For you are fully aware that the Day of the Lord will come like a thief in the night“, which for the disciples was in the context of what Jesus said when He appeared to them before His ascension-- "“It is not for you to know times or seasons that the Father has fixed by His own authority." (Acts 1:7)
And at least one verse in Revelation clearly refers to the time of the end due to the fact that it occurs in the 16th chapter at the time of the outpouring of the sixth bowl, just prior to the pouring of the seventh bowl: "Behold, I am coming like a thief. Blessed is the one who remains awake and clothed, so that he will not go naked and let his shame be exposed."
But ... there is an intriguing verse found while the Church is still on earth. Speaking to the Church at Saturday, Jesus says: "Remember, then, what you have received and heard. Keep it and repent. If you do not wake up, I will come like a thief, and you will not know the hour when I will come upon you." (Revelation 3:3). Clearly this cannot refer to the Day of the Lord as described in the latter parts of Revelation: it must refer to what could occur while the Church is still here. Is this then a reference to the unknown timing of the Rapture? The coming as a thief; ie, suddenly and unexpectedly? Decide for yourselves. I'm not making any claims or trying to establish any doctrine; I simply thought
@Goodboy's question deserved some scriptural effort.
All that said, our brother makes an excellent point-- if the Matthew (and Mark and Luke) accounts of the Olivet Discourse are to be interpreted as referring to the Day of the Lord and not the Rapture, then where in Holy Writ do we come up with the doctrine that the time of the Rapture cannot be known?