Information from the Attorney General’s website:
It is possible to shorten the minimum notice time for a marriage to less than a month if, and only if, the special circumstances set out in the Marriage Regulations 1963 are met.  You will need to approach a Prescribed Authority for approval. You may need to make an appointment, and a fee may be payable. 

Prescribed authorities are listed on the Attorney General’s website (Prescribed Authorities are usually found at your Local Court or Registry Office).  They can shorten the required period of notice if they are satisfied that the circumstances prescribed in the Regulations are met.

The five categories of circumstances set out in the Regulations are as below.
Please note that the examples are only as a guide, and even if you have the same situation, it does not guarantee the shortening approval.

• Employment–related, or other travel commitments 
    e.g.: I am scheduled to be deployed overseas for a military service in 3 weeks but we haven’t lodged the NOIM yet and we want to marry before I leave.
• Wedding or celebration arrangements, or religious considerations
    e.g.: Our wedding is in 3 weeks. We already booked and paid for everything but falied to lodged the NOIM. Rescheduling the event will make us lose a large amount of deposit, and my parents won’t be able to make it on a new date.
• Medical reasons
    e.g.: My family member is diagnosed with a terminal illness and only have 2 weeks to live, and we would like them to witness our wedding.
• Legal proceedings, and
    e.g.: The court decision may result in the deportation of my partner and we wish to marry before this occurs.
• Error in giving notice.
    e.g: We thought we had correctly given notice a month before the wedding date, but due to a clerical error, it was never properly submitted.

The reason for wanting a shortening of time for notice must fall within one of these categories. There is no capacity to grant a shortening of time outside these circumstances.
 * “We want to get married before my visa expires so that I can stay” is usually not a valid reason. I have had some couples try but none of them got the approval.

Shortening of time is NOT automatic and if your request does not meet the requirement or you don’t have sufficient evidence to support your request, your application will be denied.
When making a decision, the Registry of Births, Deaths and Marriages (BDM) or a Prescribed Authority will weigh up the information provided in support of your application and may seek additional information as outlined in the Regulations.

My fee for shortening application support is $80
(this is on top of your ceremony package and what the registry office may charge)

The service includes: 1 meeting (in Rosebery or online if you are in Australia) to explain the process and witness the signing of the NOIM, lodgement of the NOIM, application of shortening to the registry/prescribed authority, and liaising with the registry/prescribed authority to support your request.

What usually happens is this:

1. Contact me to see if I can conduct a ceremony on the date/time you want. I will explain the shortening process.
2. Complete a Notice of Intended Marriage, meet me (in person or online if you are in Australia, or meet another authorised witness in person), sign and lodge it with me.  Only one person can sign and submit as long as both of you agree on this.
3. Send me all the supporting documents for your shortening claim.
4. I will contact the registry to apply for the shortening with all the documents.
5. The registry will make a decision, usually within a few working days.