Context brings us to 1290 years in the future; not to the destruction of the Temple in 70 AD my friend. But 1290 years from the point that the Messiah is cut off on Calvary.
Matthew 24:20 is being said in connection with verse 15.
The abomination of desolation happens many years in the future from the destruction of the Temple.
Here let's take a look.
Then when you see the abomination of desolation, which was spoken of by Daniel the prophet, standing in the holy place (the one reading, let him understand),
(Mat 24:15 LITV-TSP)
And from the time the regular sacrifice shall be taken away, and the abomination that desolates set up, a thousand, two hundred and ninety days shall occur .
(Dan 12:11 LITV-TSP)
And after sixty two weeks, Messiah shall be cut off, but not for Himself. And the people of a coming prince shall destroy the city and the sanctuary. And its end shall be with the flood, and ruins are determined, and war shall be until the end. And he ( Messiah) shall confirm a covenant with the many for one week. And in the middle of the week he (Messiah) shall cause the sacrifice and the offering to cease. And on a wing of the altar will be abominations that desolate, even until the end. And that which was decreed shall pour out on the desolator.
(Dan 9:26-27 LITV-TSP)
As we can see The Messiah shall be cut off. He shall cause the sacrifice to cease (the sacrifice shall be taken away). And from that point; 1290 days and then the abomination of desolates is set up. (the one reading, let him understand),
If we use the "day for a year" Prophetic standard put forth by the LORD in Ezekiel 4:6 that brings us to 1290 years from the point in which the Messiah offered up His sacrifice not to 70AD.
So one can easily see that Jesus is saying, "Pray that your flight not be in the winter or the Sabbath day" in context to 1290 years from the point of His work on Calvary, not the destruction of the Temple.
It is also note worthy that Jesus says in Matt 24:15, "whoso readeth, let him understand". This emphasizes the point that he is speaking to those in the future. The earliest date that I can see that is placed on Matthew is 40 AD. But the general consensus is 70 to 90 AD. Either way the circulation and transcribing difficulties of it at the time would had made it virtually unheard of. Especially considering the persecution the Christians were receiving from their Judean brethren. The Christian church was not welcome in Judea my friends; let alone Jerusalem.
Also when one considers the context of Matthew 24:20. The Apostles to whom He is speaking to have long since been dead.
Here take a look in Matt 24:9 "Then shall they deliver you up to be afflicted, and shall kill you: and ye shall be hated of all nations for my name's sake."
All the verses that follow are a continuation of the same prophesy. Well past verse 24 actually. This simple fact can be determined by the uses of the words like, and, but and then. So that means that the Prophesy is more for "whomsoever readeth" than the Apostles.