How much longer till my budgie lays an egg?

Its been months since my budgie first went into the nest box and she's always went in and out. During the past few days she is now just going in there and staying in there for a really long time. She stays in there for most of her time. I know the male and female have mated. I've seen them mate a lot. Her vent is also larger and looking at her from the side, I can see that her bum is bigger. When I took her out yesterday to look at her vent, it was pink and large. Her droppings are also getting larger. I hope she is not egg bound though. So, how much longer do you think it will be? Whenever I look in the nest box, there are no eggs yet.