Reading the Scriptures a person could come to the opinion that the fall was an instant action that was a once off. But the Scriptures demonstrate that the fall actually took place over a long period of time.
We should first look at how long Adam lived. God told Adam and Eve _
"But of the tree of the knowledge of good and evil, you shall not eat of it: for in the day that you eat from it you will surely die." Gen 2:17
This word "day" means a time; and is used in regard the creation to mean one period of light and a period of darkness, by the measure that God was using for the creation (Gen 1:13). It should be noted that our sun, from which we draw time, wasn't made until days into the creation (Gen 1:16-19). So how long was this day that Adam would die within if he transgressed?
The Scriptures inform us that it was a thousand years (2 Pet 3:8, Abr 3:4). And how long did Adam live?
"And all the days that Adam lived were nine hundred and thirty years: and he died." Gen 5:5 (Also note Moses 6:12)
So in the day (thousand year period) that Adam transgressed he died, as God declared. In fact no one lived beyond the day.
Yet this didn't end the fall. The fall is demonstrated to have continued as a result of ongoing sin. The shortest lifespan before Noah was Noah's father Lamech living for 777 years (Gen 5:31). Yet Noah himself lived longer than Adam (Gen 9:29). So it took more than those generations to really show what was happening.
Gen 6:3 has the Lord declaring man's days to be 120 years. But this is put in the wrong place, because this is a long time before that became true. After the flood we see from the genealogy a great drop in the life-span from generation to generation. We see in the genealogy of Shem, the son of Noah _
Gen 11:12-13 Arphaxad lived for 438 years only.
Gen 11:14-15 Salah lived for 433 years.
Gen 11:16-17 Eber lived for 464 years.
Gen 11:18-19 Peleg lived for 239 years.
Gen 11:20-21 Reu lived for 239 years.
Gen 11:22-23 Serug lived for 230 years.
Gen 11:24-25 Nahor lived for 148 years.
Gen 11:32 Terah lived 205 years.
Gen 25:7 Abraham lived 175 years.
While this is a strange decline, it is demonstrating that the fall wasn't instant. Matter changed over the time. This change is another reason why "scientific" dating methods are useless before Moses, as the fall didn't have its full effect. No one can possibly understand what matter was like during that time, and at what rate it was affected. Particularly since we have no idea what matter was like originally (before the fall).
Also of note is that while Noah lived for over 900 years, his grandson (Arphaxad) only lived over 400 years. So obviously Noah's righteousness needs to be taken into consideration. Yet in spite of hick-ups the decline after the flood was rapid.
Moses declared that by his time people were living only 70 to 80 years at best _
"The days of our years are seventy; and if by reason of strength they be eighty, yet is their strength labour and sorrow; for it is soon cut off, and we fly away."
Considering that we live around that time now, it suggests that no further falling of matter occurred thereafter.