My wife works for the government and whenever she has to do atips she has to stop work to deal with them. I'm not sure your idea of an atip department is the most accurate...
It is my speculation. Please tell all if you have 1st/2nd degree knowledge.
Perhaps in your wife's case, there's physical papers to be sorted through, or the ATIPs are unique queries?
For GCMS, others have observed their documents were electronically generated the day after their request. With CIC's warehouses of paper(pushers), the most logical conclusion is that 1-day extraction of all the pages couldn't interrupt the process. If any human-intervention were required, it would take faaaaaar longer.
Does your wife have any say in redactions? (Assuming there's nothing requiring cabinet confidence/DoJ consultations)
I particularly like the ATIP requests listed here:
http://www.ci.gc.ca/English/department/atip/2013/august.asp
Evidently there's an immigration lawyer doing their homework. I've seen the same types of requests in 2017:
Step 1: Ask for listing of all CIC employees and their titles
Step 2: Ask for email headers for key employees between certain dates (to avoid being too broad)
Step 3: Ask for specific emails based on headers