@audistarelectronics,
I understand that worry, of course!
Looking at it in terms of business days, it's taken about 14 business days to date. While that's quite a while to wait, it isn't unusual in these bizarre times. In particular, it must be chaotic in Sydney at the moment as your State fights to contain outbreaks in an attempt to stop what's happening here in Melbourne from happening over there. I imagine that the whole chain of post offices and postal workers and couriers and deliverers is disrupted.
If tomorrow is the earliest you can escalate to a claim, I would - were I in your situation - hold off a bit longer. You can afford to hold off until 30 days from the latest Estimated Delivery Date (or, to play it safe, say no later than 25 days from the latest EDD, or whatever timeframe best suits you). You say that the seller is a reputable B&M store, so your issue is certainly not with a fear that the seller is stringing you along, but rather with what appears to be a postal delay.
Have you tried phoning Australia Post? You can also make an online enquiry where the online form is sent to AP with your concerns. From experience, I can say that AP will almost certainly contact you quite soon after that, and do their best to give you any updated information.
If this is a seller from whom you enjoy purchasing, and from whom you'd like to purchase again, bear in mind that the seller may consider buyers who raise disputes during a time when postage timeframes have ballooned and everything is especially chaotic to be buyers with whom they'd rather not deal in future.
You'd not be losing anything by holding fire for, say, another week, and certainly by chasing up AP to see whether they have additional details about where the package might be at this point.
You'd be within your rights to open a dispute once the system allows you to. My view is simply that you have a 30-day window from that time to open a dispute, and there is good reason to suppose that postage delays due to COVID-19 are affecting delivery times... hence I would be holding off at this stage.
Whatever decision you make, remember that you're covered. Your $300 is not going to be lost, whether you open a claim tomorrow, or whether you open the claim a little later (or up to 30 days later).
If it helps, I'm only just now receiving some items that I'd ordered three weeks ago from major retailers in NSW. (I'm in outer metropolitan Melbourne.) I expected the delays and was not perturbed by the slow delivery times.
Good luck!
