Gap theorists have tried for decades to move Satan's fall before Genesis 1:31. The biblical evidence is too great to overcome.
‘You were the seal of perfection,
Full of wisdom and perfect in beauty.
13 You were in Eden, the garden of God;
Every precious stone was your covering:
The sardius, topaz, and diamond,
Beryl, onyx, and jasper,
Sapphire, turquoise, and emerald with gold.
The workmanship of your timbrels and pipes
Was prepared for you on the day you were created.
14 “You were the anointed cherub who covers;
I established you;
You were on the holy mountain of God;
You walked back and forth in the midst of fiery stones.
15 You were perfect in your ways from the day you were created,
Till iniquity was found in you.
16 “By the abundance of your trading
You became filled with violence within,
And you sinned;
Therefore I cast you as a profane thing
Out of the mountain of God;
And I destroyed you, O covering cherub,
From the midst of the fiery stones.
17 “Your heart was lifted up because of your beauty;
You corrupted your wisdom for the sake of your splendor;
I cast you to the ground,
I laid you before kings,
That they might gaze at you.
18 “You defiled your sanctuaries
By the multitude of your iniquities,
By the iniquity of your trading;
Therefore I brought fire from your midst;
It devoured you,
And I turned you to ashes upon the earth
In the sight of all who saw you.
19 All who knew you among the peoples are astonished at you;
You have become a horror,
And shall be no more forever.” ’ ”
Satan did not fall until after day 6, after Eden was created. He had liberty to move back and forth between Eden and the heavenliness, prior to his fall.
And it's very clear the symbolic curse on the serpent was, in reality, Satan's fall and curse.
Gen. 3:14 So the LORD God said to the serpent:
“Because you have done this,
You are cursed more than all cattle,
And more than every beast of the field;
On your belly you shall go,
And you shall eat dust
All the days of your life.
15 And I will put enmity
Between you and the woman,
And between your seed and her Seed;
He shall bruise your head,
And you shall bruise His heel.”