I think another thing to look at in the passage you are referencing and seem to be stuck on for meaning is that the context of that lesson about the gathering has to do with that people don't know when Jesus is coming. People can and will be ignorant. Even when that day comes, and the prophets tell us it will be a day unlike any other, no one knows the hour. I think it will go on long enough that people will eventually go about their normal business. At some point, someone is going to say, 'Well it may be dark out, but someone has to get something to eat,' or 'I'm tired; I'm going to bed.'
ZEC 14:3 Then the LORD will go out and fight against those nations, as he fights in the day of battle. 4 On that day his feet will stand on the Mount of Olives, east of Jerusalem, and the Mount of Olives will be split in two from east to west, forming a great valley, with half of the mountain moving north and half moving south. 5 You will flee by my mountain valley, for it will extend to Azel. You will flee as you fled from the earthquake in the days of Uzziah king of Judah. Then the LORD my God will come, and all the holy ones with him.ZEC 14:6 On that day there will be no light, no cold or frost. 7 It will be a unique day, without daytime or nighttime--a day known to the LORD. When evening comes, there will be light.
Likewise, the people in Noah's time didn't know the flood was coming. To some, especially the wicked, this day will catch them unaware. They will be "left behind." I think too that even those that are to be gathered up with the elect do not have to have perfect knowledge of what is going on. You do not have to pass an eschatology test to be admitted to Heaven. So the theme of Mt 24:36-41 is that people will not know exactly when this day will come.
I will reemphasis, that even though Jesus gives us a series of events that precludes the sign of the Son of Man and the attendant gathering of the elect, there is enough latitude of time regarding what Jesus remarked as being a great tribulation unequaled in time that it is impossible for anyone to predict which particular day after the midpoint when the Abomination is set up when the words of Ezekiel come true:
EZE 32:7 When I snuff you out, I will cover the heavens
and darken their stars;
I will cover the sun with a cloud,
and the moon will not give its light.EZE 32:8 All the shining lights in the heavens
I will darken over you;
I will bring darkness over your land, declares the Sovereign LORD.
This might be my problem. In Matthew 24:39, this is the group that is taken, that means Noah was left behind.
"And knew not until the flood came, and took them all away"