Correct me if Im wrong, but in the futurist world this passage is a vision of after the rapture, with Jesus speaking during the so-called tribulation period.
14 For they are spirits of demons, performing signs, which go out to the kings of the earth and of the whole world, to gather them to the battle of that great day of God Almighty.Are you just cherry picking verses?
15 "Behold, I am coming as a thief. Blessed is he who watches, and keeps his garments, lest he walk naked and they see his shame."
16 And they gathered them together to the place called in Hebrew, Armageddon. (Rev. 16)
The day of the Lord is used 19 times in the Old Testament and 4 times in the New Testament. It isnt used in the same sense or reference each time. I would contend that trying to tie the term to either the Rapture or Armageddon or anything else every time it is used is error.