Ann: Trading Halt, page-296

People need to calm down and stop jumping at shadows.
The trading halt text and all timings involved are totally normal.
They absolutely had to do a TH, it was never optional.

ASX trading rule 16.4.2 limits the length of a trading halt until the beginning of normal trading the second day after the trading halt request.
So there is absolutely nothing unusual about the specification of Monday - it's pretty much the copybook text for a trading halt.

This usually means that the company will announce prior to that time - but you can't know when that will be, some companies do it in a few minutes, some run all the way to that day.
In some instances if you don't have the event ready for announcement prior to the recommencement of trade the ASX may suspend your entity from trading to avoid a disorderly or uninformed market.

So we have pretty much learned nothing by the text of the ASX notice.

What might have happened:
1) The company decided to suspend trading in US and OZ until they receive word from FDA, sensibly limiting any chance of leaks occurring before proper notification to the market. In this case they are still waiting for the official FDA notice and the FDA is late (thought it's still 30 Sept in USA right now). If the FDA is very late, we may resume trading with an announcement that they have not received any advice from FDA and are awaiting that advice which is overdue - many companies have had that happen during Covid.
2) They did receive a notice from the FDA and will announce some time today whatever the result of it is.
3) They received notification from the FDA that they will receive something soon - which means they are waiting too.

Guessing scenarios without any further data is a waste of time.