Yes, you can receive AOR on a Saturday. IRCC communications are often sent out in batches and not in "real time". Many people receive AOR and other notifications on the weekend. I personally received my PPR on a Saturday. It doesn't mean there is somebody sitting there in the office sending it to you at that very moment - rather, it was previously queued up to be sent out during business hours and the weekend is when it ended up being sent, in an automated fashion. Likewise why you might see MyCIC or ECAS update on a Saturday. The updates were pushed through during the week, but only happen to become visible on that day.