About HK Visa

Hi, I'm holding Vietnamese Passport and I will go back to vietnam for chinese new year on 20th Jan 2012. I planned to go to Hongkong on 1st of Feb 2012 so I guess that I have to apply the Visa from now or asap in Australia (I could go back to my country and apply for the visa there but the time won't be enough for visa processing). In the list of requirements, I saw that I also have to submit the Flight Itinerary. Can I apply for the visa first without this document? cos I will buy the ticket later when I got back to my country. And, If I apply now ,could I get my visa before 20thJan 2012??
Thanks so much for your help!!