On the 5th of March, 2012, the Iranian Attorney General announced that the conviction and death sentence were overturned. They were deemed “incomplete”. Whatever that meant.
What it meant was that the onus of the death sentence was gone. Amir was in a grey area, and would remain so for some time. He was still in solitary confinement, but not as horrible conditions as before his initial conviction. 
This new hope caused the family to make plans to come visit Amir. I am not sure when he was told, and from reading reporting from other people who had been confined in Evin, I am inclined to think he was not told right away.