The answer is dependent on the number of subjects that you take each semester. Essentially, studying a degree part-time is assumed to take twice as long than if a student were to study the same degree full-time. In the case of the Bachelor of Commerce, this means that it would take 6 years part-time to complete. Of course, this duration is established based on the assumption that a student would be taking two subjects per semester, as opposed to four each semester (which constitutes a full-time study load).
Given that there is no minimum requirement for the number of credit points per semester, you could take as little as one subject (6 credit points) per semester. However, this would extend the duration of a Bachelor of Commerce to 12 years, which would be highly impractical. The most time I have seen someone take to complete a business degree is 8 years and that person was a mature-age student with a family to take care of, and even that is still a substantial amount of time to take to complete a 3-year degree.
If you take 3 subjects per semester (i.e. 18 credit points, which USyd considers the minimum for a full-time load), you would still be completing your degree full-time (making you eligible for government payments such as Youth Allowance), although it would take you an extra year to complete the Bachelor of Commerce, and technically (i.e. unofficially) you would be a part-time student.
Overall, the actual duration of the Bachelor of Commerce will depend on the number of subjects that you take per semester. The minimum duration would involve a full-time study load and is 3 years (assuming that you do not enrol in more than 24 credit points/4 subjects each semester). Otherwise, the lower the number of subjects that you take each semester, the longer it will take you to complete your degree.
I hope this helps!
