Mystery of staggered AOR's receipts solved. I called into the helpline to change my telephone number and the agent was very helpful in answering other questions.
I was told that the applications are stamped with a date stamp on the day they arrive and stored. Thereafter, applications are removed for initial review from the storage within date ranges i.e. Applications received between 03 May and 10 May are batched together and assigned to agents for initial review and entering the details in the case. Multiple batches are handed over to different agents. The same agent is processing other category of applications as well i.e Permanent Residence Renewals, Express Entry, Spousal Visas etc. When agents start processing the batch for initial review, they can come across the more recent applications in the batch first basis how they were batched together. As such, an application received on 10 May be opened for initial review prior to the application received on 03 May as they are in the same batch. Some agents may process files for initial review sooner than others. The initial review of AOR is impacted by how the files were batches, the load of other category of applications, the speed with which the agent processes the initial review, holidays, weekends, the quality of the application filing process by the individuals.
Agents input information online by 1500 hrs local time and the system populates and updates the details on the web portal between 1800 hrs- 2200 hrs local time EST every day. Automated notifications are immediately issued but ECAS updates takes anywhere from 12 - 72 hours. ECAS is updated within 72 hours and if the file is updated in ECAS, the processing centre is already assigned by then. The file then physically travels to the processing centre on a weekly basis for processing review.
As Obannobi mentioned in a previous post, the agent confirmed the processing time is not linked with the AOR, Some applications are processed faster while others are processed slower. The administrators can see the case load and assign case files accordingly. The assigning of case processing centres already incorporates equitable distribution of files across provinces and cities.
Hope this helps those are are anxious about their AOR and processing status.