Hi...,
If you are requested further information then it’s important to provide the requested documents in a timely manner and you are normally given 28 days. When the documents are returned the case officer will genuinely have a pile of applications that are awaiting further documents and will be working through that pile in receipt order. So the longer you take to send the document in the longer it will take for a decision to be made. The same process explained here will apply to any further requests the case officer may make as the case officer may have further queries form the documents provided.
Once the case officer has everything to make a decision they will normally grant the visa within a few days. However the time taken for the case officer to review the file once assigned or granting of the visa can depend on a number of factors such as their work load, their holidays, sick days, public holidays and in some cases Department of Immigration and Citizenship (DIAC) officers work job share so are only in the office 2, 3 or 4 days a week.
It is important to note there is no need to email or contact DIAC to make further enquiries as this only delays the process further. The more time taken replying to enquiries means less time for working on files. So, it's better contacting the CO in emergencies or the case officer is taking an extended period of time to grant the visa once all documents have been provided.
Hope this helps