Well, the good news is that today's date will, in essence, be your official AOR date.
The bad news, is that it will likely be at least a month before you get the AOR email...if at all.
Some people never get the official AOR notification from CIC, so all they have is their delivery confirmation date (proof of delivery receipt) to calculate the processing time by.
It's important to note that if your application is returned, due to an outdated form, missing signature(s), or even something as ridiculous as the clerk, that opens your parcel, seeing that you mistakenly included IMM 5669 for the sponsor (because s/he thinks you didn't follow the directions on the Document Checklist)...it would add several months to the process. We've seen applications returned for all sorts of reasons, of which some were valid reasons...some.
Once CIC issues the AOR, it means that someone opened up the package and has determined that all required forms, signatures, etc., have been submitted. It's really nothing more than a cursory glance at everything.