Rehabilitation at an embassy can take anywhere between 6-12 months, but it depends on the urgency you need to go to Canada. For Americans they can actually get these issued at land crossings in a matter of days. However, as an Australian you won't have this option. Generally if 5-10 years have passed you are eligible for rehabilitation. In fact for many convictions you are often deemed rehabilitated after 10 years and you don't even have to submit a rehabilitation app. My wife a traffic offence and after 5 years had passed, I submitted the rehabilitation app for her and she was granted it in a couple of weeks (but this was at a land border crossing with Canada). In all honesty they really just look for the adequate time that has passed. Once that is rubber stamped everything else is just to make them look like they know what they are doing.
In a worse case scenario and you are not granted rehabilitation ( I don't see this happening) , you can apply for a TRP (temporary resident permit). This will allow you to enter Canada if you do not qualify for rehabilitation. These can be granted for a few days or up to a 3 years! If you are granted a TRP for a year or longer you can actually apply for an open work permit and live and work in Canada for however long your TRP is good for, it is also renewable. You can also submit a TRP application simultaneously with your Permanent residency application so if in a worse case scenario and they deny your PR based on criminality, they will often grant you the TRP for 1-3 years.
As a Canadian I do apologize for our system it is very overzealous and makes no logical sense. I wish we had Australia's system, you have to do serious jail time (I think 5-10 years) before you are automatically denied entry.