The time was selected to allow the Pies to fly home and sleep in their own beds.My guess is that it's so it doesn't clash with the NRL semi on at the SFS (basically next door) this evening, but yeah it might be so they can get a flight home this evening rather than tomorrow.
Long standard protocol to not disadvantage the prelim away team for next week's dance.
Of course it doesn't matter if the Pies do not win.