Application processing times vary and the time it takes to finalise an application is affected by a range of factors outside of the department's control. In respect of applications for a General Skilled Migration (GSM) visa, many applications will be affected by the Ministerial Direction which lists the order in which GSM applications must be processed.
See:
Visas for Migrating to Australia as a Skilled Person – Application processing times
Critical Skills List ( 54KB PDF file)
What's New? Recent Changes in General Skilled Migration
Note: Incomplete and some individual applications may take longer depending on the completeness and complexity of the case.