Just found this in the 'exam navigator', for anyone who may have a timetable clash as well:
Students may have a timetable clash (two examinations at the
same time) for examinations on a particular day. If so, students
may apply to the VCAA through their school principal to move
one of the examinations to another time on the same day. This
written request must be made by Friday 23 July.
All examinations must take place on the date as published in
the timetable. Students with an examination at an alternative
time must also be supervised between the two examinations.
If no correspondence is received prior to the commencement
of written examinations, the VCAA will contact the schools to
advise them of the scheduling of the two examinations.
Note: This is from the 2010 version, but I'd assume the date
would be around the 23rd July for final applications.