12h 30min, jul 31, 1991 y - Quirrell attempts to steal the Philosopher’s Stone from Gringotts
Description:
 He is directed by Voldemort to attempt to steal the Stone, but he fails. As a result of this failure, Voldemort decides to possess Quirrell in order to control his actions more closely. 
Added to timeline:
Date:
12h 30min, jul 31, 1991 y
Now
 ~ 34 years ago