Initial Entry to Australia after a migration visa has been issued
A migration visa will allow you to travel back and forth from Australia with no restriction, allow you indefinite permission to remain in Australia and is valid for five years. Prospective marriage visas are valid for nine months and provisional spouse visas are valid until a decision on the permanent visa is reached.
ALL such visas are issued on the condition that the holder enters Australia at least once before a certain date, and once a such a visa has been issued, this INITIAL ENTRY DATE cannot be changed under any circumstances.
As part of the migration application process, medical examination results and police clearance certificates must be provided to assess if the applicant meets the health and character criteria that are stipulated in the Migration Regulations. Both the medical examination results and the police clearances are valid for one year.
All migrants are required to make their initial entry to Australia within the validity of their medicals and police clearances and there are NO exceptions to this whatsoever.
Not complying with the initial entry condition would render your visa liable to cancellation and if you still wished to migrate, you would have to apply for a new migration visa. You are not required to migrate to Australia before the initial entry date, although of course you may, but you are required to make at least one entry to Australia in whatever capacity you choose before the initial entry date expires.