I could be mistaken - I am not an instructor, just a lowly DM - but if you were taking the PADI advanced open water, a night dive is not required. There are a lot of different type dives they can teach and do to make up the required five dives. For example, you can do a drift dive, underwater navigation, underwater naturalist, navigation, deep dive, dry suit dive, altitude diving, boat diving, search & recovery, peak bouyancy, night dive, etc. You have to do five of these and the only ones required are the navigation dive and something called the "adventure" dive.
I feel for you though as the one of the most common AOW dives is the night dive and it's good to learn it then. PADI allows you to do night dives even without the training and most shops will only want to see you are an AOW before allowing you to do a night dive with them. They won't check that you have the training although it's a good idea to get it when you do your first night dive. Depending on where you dive, just talk to the DM/instructor on your next trip and they should help you out without any further cost.
