I'd get rid of the infrared globe (no idea why anyone ever wants to use those ridiculous things!) and replace it with a visible light spotlight. They're much cheaper and better for a blue-tongued. The sun produces light, that's what is natural and what a blue-tongued will respond best to. It's a cue saying this is a good place to bask and get warm.
I think 24 degrees is stupid, unless you're trying to force the lizard to hibernate, which I personally wouldn't do with a juvenile. It may be a strategy some people would use for adults for a short period in the middle of winter (winter hasn't started yet, and the dead middle of winter isn't for about two months).
I personally would still give him a basking spot of over 32 degrees. For a juvenile I wouldn't bother trying to provide a winter in his first year (other people would, that's personal preference and you may choose to). If anything, I would personally only give maybe 2-3 weeks of simulated winter, in July. If you do want him to stay active, feeding and growing through winter, you'll need to give him the temperature required to do that.
I'm not personally an advocate of copying nature as closely as possible (the vast majority of wild reptiles die before 1 year of age, have scars, parasites, very rarely live to old age, etc... I really think we should be aiming to do much better than nature!) but for a beginner keeper with a blue-tongued lizard, some aspects of nature are worth considering. When it's cold at night, they just go to sleep, they aren't metabolising much so the temperature isn't too important during those hours where it's too cold, as long as you're not silly about it. If you want him to be active and feed he'll need an opportunity to get above 30 degrees, preferably 35-40 degrees in a basking spot provided by a spotlight. In nature, if they want to warm up, they go sit in a sunny spot. At this time of year, the air is cold, but the sun and the rock/log/ground they are on is hot, heated by the sun which puts out visible light. The best way to simulate that is to provide a spotlight, and you don't usually need to provide any other heating. He'll heat up in the basking spot then when he is warm enough he'll run around foraging for feed and exploring. He may or may not understand a dark infrared heat source, or use floor heat (you won't find magical heated patches of ground in the shade in Melbourne, or anywhere without active volcanoes etc). If your plan is to keep him active through winter, give at least 8-10 hours of basking light per day where he can easily get above 30 degrees, preferably more. It's pretty easy to do this, just arrange the enclosure so a rock or log is close enough to the spotlight (experiment using an infrared thermometer to see how hot the rock gets). To give you an idea, when I was breeding small monitors I used a 40-60W spotlight to provide a basking spot of 70-80 degrees, which the lizards loved and used every day. Blue-tongueds aren't quite as extreme but I'd personally give them at least a 40 degree basking spot, along with a fairly cool ambient temperature, and depending on the temperature of the room etc, little to no floor heat (with most snakes I love floor heat, but for some such as Tigers, Red-bellieds, Copperheads and other southern, diurnal, cold-adapted snakes which have fairly similar thermal habits to Blue-tongueds, ideally I'd do the same).
Basically, in south eastern Australia these lizards are either giving up and going into deep hibernation, or they work as hard as they possibly can for most of the year to get as hot as possible, and ideally they want a body temperature of somewhere around 30/low 30s, and since the air temperature is below that most of the time, they need to find basking spots much higher than their preferred temperature to get to their preferred temperature. If the opportunity to get warm enough doesn't exist, they usually won't risk their lives trying (a lizard out in the open too cold to move properly is very easy prey!) so they will just crawl under a big log and wait for warmer weather.