If you want to formally change your surname, you need to apply to BDM for an official marriage certificate. The one you receive on your wedding day from your celebrant is a commemorative one only. You can start using your new surname in social circles from your wedding day which is exciting! But you can't formally change it (eg: passport, drivers license) without the official BDM issued certificate. And if you're booking honeymoon tickets for straight after your wedding, book them in your maiden name to save confusion and hassle at the airport!
If you married in Victoria, jump online to apply here: Births, Deaths and Marriages Victoria. If you are married outside Victoria, you will need to apply to the appropriate Registry of Births, Deaths and Marriages in the State or Territory in which you were married.
Registration times vary depending on the time of year. It's usually about 4 weeks during non-peak wedding season. During peak wedding season, (October to April) it can take up to 8 weeks. Your celebrant will send your papers off to BDM within 14 days of your wedding so just make sure you leave a bit of a gap to allow for BDM to receive and register your wedding before you apply for the BDM issued marriage certificate. The wait time after applying for the certificate varies, but it can take up to two weeks.
When you have the BDM certificate in your hands, you can go about changing your name with the millions of organisations that you are registered with! The first place to start is your passport and drivers license. Once you these are done, you can take these documents to the various places to get the rest of the name change game done - eg: medicare, your bank, mobile phone, gas bill, Citylink...the list goes on and on and on.....!
Feel free to get in contact with me or head to the BDM website for extra reading.