Yes. As long as your Placement Coordinator approves your start date and you have been officially enrolled into the relevant placement unit, you can start before the official start of teaching for your placement unit enrolment. You must get this approval in writing (i.e. email to education@cairnmillar.edu.au) from your Placement Coordinator and ensure that the correct start date is noted on your Form A (try to get that completed early too if you can – this is especially important for early start dates for insurance reasons).
You still need to have all of your pre-placement paperwork in order. See: Can I start my placement if I haven’t provided a police check, working with children check etc
Note: your active placement activity must start before the Census Date for your enrolment. If you cannot start before the Census date then you need to request an enrolment transfer to the next available enrolment period before the census date. See: Special Enrolments (e.g. Manual Enrolments) and What is the Census Date?