When a .au domain name is registered, it can be transferred between registries immediately (unlike GTLD domains, which have a 60 day embargo period). Your .au domain is always registered for a two year period - .au domains cannot be registered for a longer or shorter period than this.

Renewable period before expiry

Can only be renewed up to 90 days before the expiry date for up to a 2 year period

Renewable period after expiry

When a .au domain expires, it can be renewed without penalty for 30 days after the expiry date.

1. DNS propagation of your domain name will fail to resolve during this period, as a result any mail delivered to your account or users viewing your website will not be accessible;
2. The domain name cannot be updated;
3. The domain name can be renewed or transferred to another registrar;

Deletion from registry

30 days after the expiry of the domain name, the domain will enter the status of "Pending Delete" for a 3 day period

1. DNS propagation of your domain name will fail to resolve during this period, as a result any mail delivered to your account or users viewing your website will not be accessible;
2. The domain name cannot be updated;
3. After the domain is deleted from the registry it will become publicly available for registration again;

Source: http://www.auda.org.au/policies/index-of-published-policies/2010/2010-01/