The AoR arrives by e-mail. Before the pandemic it use to take max 3 months, but nowadays it is taking even more than 7 , 8 months.
I applied in march and still waiting.....
Funny, how even with 7 or 8 months for the AOR, the processing time is now 22 months instead of 23...
I have just checked it
here
Maybe in the end the long waiting time for the AOR doesn't influence at all the processing time.
From the IRCC website:
"A processing time starts the day we receive a complete application and ends when we make a decision. If you apply by mail, the time starts when your application arrives in our mailroom. " - To my understanding, they calculate it from the day the courier or the post delivers the parcel.