You are misunderstanding Revelation 12:9, thinking that passage indicates that Satan is not now on this earth. Satan is on this earth, and also the second heaven (the cosmos) - and he currently has freedom of movement between the two.
When the future war in heaven (the second heaven) takes place, it will be right after the two witnesses come back to life and ascend to heaven (the third heaven).
There is the big earthquake in Jerusalem. And the 7th trumpet sounds. It is not at the end of the 7 years as some reason, because they are not understanding it says the kingdoms of this world "are become" the kingdoms of God and His Christ. It a process is that starts of taking away Satan's dominion overshadowing this world.
The kingdoms of this world becoming the kingdoms of God and his Christ - that
unfolding is the mystery of God that should be finished, in Revelation 10. John is given a little book to eat, and that the contents of that book is what we read in Revelation after chapter 10. The seventh trumpet is not at the end of the seven years; it is at the mid-point, just a the person has become the beast and just killed the two witnesses. Which, God at that point has become fed up with Satan and begins to prosecute him and his kingdom. Beginning with casting Satan down to earth.
Revelation 10
6 And sware by him that liveth for ever and ever, who created heaven, and the things that therein are, and the earth, and the things that therein are, and the sea, and the things which are therein, that there should be time no longer:
7 But in the days of the voice of the seventh angel, when he shall begin to sound,
the mystery of God should be finished,
as he hath declared to his servants the prophets.
What God declared to the prophets is that His Kingdom would come to earth and rule over the kingdoms of men. In Daniel 2 it is in the days of the ten kings of the fourth empire. In their time, God will setup his everlasting Kingdom here on earth.
The ten kings' time is in Revelation 17:17 as their pledge their kingdom to the beast for that last 42 months in Revelation 13. The ten horns have their crowns in Revelation 13:1, signifying their rule will the beast the 42 months. During that 42 months, Satan will be restricted to here on earth. Right now, he has freedom of movement.
The first action of the kingdoms of this world becoming under the rule of the kingdom of God, - instead of the kingdom of Satan - in that process is to take away Satan's place in the "second" heaven. That's where the war will take place. Satan and his angels don't reside (not allowed to) in the third heaven because it would be chaos there.
The second heaven in the cosmos. It says in Revelation 12, that their place would be found there (heaven) no more. Not only Satan and his angels will be cast down to earth, but the place of their residency, the cosmos, will be removed in Revelation 6, the sixth seal.
What the status of Satan is right now is that he is not restricted to this earth. But that doesn't mean that he doesn't roam this earth as part of his freedom of movement.
"the evil day" is just saying this time in history, which has been since the garden of eden fall. The evil day exists because Satan is allowed to roam around creating trouble. When Satan and his angels are cast down, it will still be the evil day - and will continue to be until Satan is bound and cast into the bottomless pit.