How long (on average) does a dependent visa application take to go through?
On average, they used to take about two to three months. There are recent changes on the immigration department, so it looks like it could take a bit longer.
It’s not a bad idea to check with the immigration department weekly, although they might say they will contact you when it is ready. Checking in person is also not a bad idea, if it is super polite. You will definitely not achieve anything by demanding.