How long did Saphira stay in her egg from the day it was laid by her mother?
see the edit I just made to my answer, should be in time for your deadline– ibidJun 1, 2022 at 6:00
A little bit over 100 years
Saphira was born shortly before the Fall of the Dragon Riders
Was Saphira's egg laid immediately before/during the Fall, or did it happen a significant amount of time before that?
Christopher Paolini: It was laid fairly close to the Fall.
The Fall of the Dragon Riders ended one hundred years before Eragon found Saphira's egg.
So Saphira spent a bit over 100 years in the egg. Perhaps something like 105 years.