Garry,
    Yes, that is a very interesting thing, indeed!
I really enjoyed this letter of yours, like I did the other one.
It caused me to think, again, about a question that I had just asked today, as well.
So, based on what you wrote, I'll modify the question to your description:
Why did an omniscient Almighty have to shorten the days from 1290 days to 1260 days?
Clearly, from the foundation of the world, the LORD knew about the 1290 days & the 1260 days.
Clearly the LORD knew from the foundation of the world, that he would shorten the days.
Why shorten 1290, and not, rather, call it only 1260, from the beginning?
Could it be, that he wrote all this down, along with Matthew 24:20, to encourage them to pray?
He said to pray that their flight not be in the winter, so clearly their prayers can affect the timing.
Otherwise, why would Jesus say to pray for that?
Therefore, within that context, is it a hint, to those who will be in those days, to pray that he shorten those days?
If so, then it appears that will do so, as he does say that he will shorten the days.
The LORD doesn't need to recalculate, and he didn't make a mistake requiring the need to shorten the days, afterwards.
The LORD doesn't need contingencies, or "Plan B"s.
No, he is omniscient, omnipresent, and omnipotent, he is totally in control of the future, from the beginning.
The LORD responds to people's repentance or prayer, and has at times changed what he said he will do.
Jonah prophesied that Nineveh was to be overthrown in 40 days, but they repented, and he postponed judgment.
Or like how he responded to that woman who said that even the dogs eat the crumbs from their master's table?
So, is it possible that the shortening of those days will be in response to the prayers and cries in those days?
        Gino