Quirrell gör det ganska klart att det var efter det misslyckade inbrottet vid Gringotts.
“He does not forgive mistakes easily. When I failed to steal the stone from Gringotts, he was most displeased. He punished me… decided he would have to keep a closer watch on me.…”
Quirrell’s voice trailed away. Harry was remembering his trip to Diagon Alley — how could he have been so stupid? He’d seen Quirrell there that very day, shaken hands with him in the Leaky Cauldron.
Harry kunde skaka hand med honom, vilket betyder ingen Voldemort. Senare sårar hans ärr för första gången när han tittar på Quirrell vid öppningsfestet. Ergo, det var någon gång i tiden.