Hi Jelly,
The VRD can last up to any time, I've met people who went home after the whole day ended at 4pm for them, and others were still there at dinner time. When I went to my VRD in MEL last year, I was just leaving at almost 6pm. It is wise to book the latest flight possible, last year I met a girl at the interviews who was cutting it so very fine to make her flight back to Adelaide, that she had to change it because she was still waiting to do her 1 hr interview.
Good Luck for your interview!
