For someone who spends most of his spotting time at night I'm surprised you have not noticed these night freighters around Sydney sooner, I was hoping you would catch one sooner or later as I would be if I had your equipment.
The BAe 146's generally arrive Mon-Thurs near 11pm, there is normally two from two different places. I'm not sure when they depart I'm pretty sure they are the same ones that depart around 4am-5am. These aircraft operate primarily to Sydney at night, they also can operate during curfew meaning it's very hard to catch them in daylight as they need to go tech or have a Cobham machine operating for them.
Other frieghters at night are the AaE 733's that arrive use to arrive around 8:30pm and out around an hour later and Toll 733's too with a similar schedule. There is a Cessna that does Canberra-Sydney-Canberra too but I can't remember what type it is.