I agree with og and Blackcloud; I myself often do similar to depending on my time requirements. (e.g. When time permits, I would book a 7pm flight over a 5pm simply due to the better chance of a better soft product.)

Yes, the most likely time to experience the better offerings of Qantas business on such a short flight can indeed be based around a 7pm departure.

Such a flight would commence boarding after 6:30pm so to be in a situation to review these benefit, a 4:30pm lounge arrival (check in at 4pm) if you have the time.

Of course that could attenuate somewhat the possibility of much useful evening time at the destination.