I'm in inner Melbourne, and there is a fair bit of pollen and nectar coming in, so I'd add on a super, just to be sure. Even if there is not a large group of gums flowering locally, there will always be something happening in people's gardens, so better to play it safe. If you had booming hives I'd say it's urgent to get them on, but is sounds like yours are still building up, so it's unlikely they will run out of space in a hurry, so take your time. A good check it to gently lift the back of the hive on a regular basis. Over time you will get to know what is heavy and what is light, and if you check every few days you will be able to tell when it's time to super.