It depends.. sometimes in 1-2 weeks or may be months. You can email them that you want to change it to in-person. This is written in the oath invite email
I think most of the July applicants had received their AOR in Aug/Sep , I think you should call IRCC to enquire whats going on. Did you check your IBOX/junk emails whether IRCC tried to contact you?
https://www.canada.ca/en/immigration-refugees-citizenship/corporate/publications-manuals/discover-canada.html
This is the official study material. You can download the pdf.