The QF way to get an evening arrival into SYD is to fly LHR-PER-SYD.
QF10 arrives in PER around midday, making for a shorter day if you were to stopover.

If you were to continue straight through, the connecting PER-SYD flight (QF650 in southern Winter gets into SYD at 20:40 or QF652 in southern Summer gets into SYD at 22:30) arrives in the evening.
Bonus points for the option to take QF656 once a week at certain times of the year (e.g. Thursdays in November) as it's 789-operated and arrives in SYD at 21:55.

An alternative would be to fly LHR-CDG/FCO-PER-SYD, which are 789 operated all the way from CDG/FCO through to Sydney, arriving at 16:25 (southern Winter) or 18:40 (southern Summer).