You will get it once the school uploads a new batch of applications from AADSAS and decides to send out a request for your secondary. Each school does this at different times.
You have to check with each school. Some require a secondary application and/or fee from everybody, and with the volume of applicants they may not remind you or ask for it specifically. I suggest perusing each school's website or calling if you're not sure.
Some schools want that sent at the same time. You should go to the schools website anyways and look at their admissions requirements, it will also tell you what to do for the secondary.
Send your secondary when you submit AADSAS. At the same time, not before. You can send it later but you will look lazy. Still, go to the schools website, which you should have done already, and see what they want in terms of secondary applications and fees.