When will my gouldians start to breed?

I'm wondering when my gouldians will start to mate and breed i have had them now for 1 week but they have been with zebra finches for half the time i only just got rid of the zebras so they can have a chance to breed and they are starting to sing a little bit and inspecting the boxes so just want to know when they will start to mate? I have 2 male and 2 female birds in a aviary