See http://www.smh.com.au/national/educa...20-gvod9b.html

Partially quoting the article
Ahead of the 2018 application process, the Universities Admissions Centre has abolished the "main offer round", under which more than 44,000 students received offers for university courses on January 18 this year. Instead, it has established a "December round" on December 21, 2017, just five days after ATARs are released and six days after students learn their HSC results, and a ''January round" on January 12, 2018, a week after IB results are released

Details on this and other changes are at http://www.uac.edu.au/documents/scho...admissions.pdf