What happens if your visa expires and you find yourself unlawfully present in Australia? Apart from leaving the country, the range of further visa options open to you are severely limited. The general rule is that you need to have a valid visa to make a valid application for another visa.
Two of the exceptions to that rule are a spouse visa or a visa to allow for medical treatment. Both of those require applicants to comply with “Schedule 3” of the Migration Regulations, and that effectively means the application needs to be made within 28 days of the expiry of the previous visa.
A recent decision of the Full Federal Court makes it clear that schedule 3 means what it says for medical treatment visas (see Ahmad v Minister for Immigration and Border Protection (No 2)  FCAFC 200).
In relation to spouse visas schedule 3 can be waived if there are compassionate and compelling circumstances. Please contact me if you need advice on these issues.