I asked at check-in today, and the friendly agent told me they officially open at 18:50, which is three hours before departure. She also mentioned early check-in and said that they will open early if they have staff avaialble, but they do not know in advance and there is no place to call and ask.

QF F lounge was nice. À la carte dining was quick, efficient and attentive. The food selection is not huge and many items are a bit strange for a westener, but overall I was very satisfied.