sure, there is a point in the night when coal powered generators need to be running(because they have a long ramp up time) but demand is low enough that gas plants aren't running so electricity is cheap.
Eg. At 2am in Queensland it will be 8c/Kwh
https://www.aemo.com.au/Energy-systems/Electricity/National-Electricity-Market-NEM/Data-NEM/Data-Dashboard-NEM