"but I don't see why it's necessary for gaggles of overseas students to conduct night circuit training over Melbourne after 8pm."
Because it needs to be dark to do night circuits. Last light tonight is 8:22pm, mid December it's around 9:10pm, mid-January it's approx. 9:15pm and mid-Feb it's around 8:45pm.
Now maybe you can see why it's necessary.