click on the clock in the bottom right of the windows screen, Set your timezone correctly

The time zone is correct - it's only n Thunderbird that this date and time are wrong??

Well I am in South Australia as well and I have no issues with times.

However there is a rare issue that might be in play. Comes from old software usually.

Do you have the TZ time variable set?

Open a command prompt by typing cmd in the run/search box on the start menu and pressing enter. Type %TZ% and press enter. Is the error

'%tz%' is not recognized as an internal or external command,  operable program or batch file.

If not it should give a value in the error.

NOTE: The date on email is derived from UTC time + or - the offset. In he case of South Australia +9:30. The TZ variable can over ride this, but most significantly of all the date and time displayed is set by the sender. Spammers often set the date to days in the future. Make sure their mail in on the top of incoming mail sorted by date.

Another source of trouble are sender with incorrect date and time information. The old adage garbage in garbage out applies here. But that is usually a single sender or in extreme cases a domain.

What mail provider? A few years ago I had trouble with Bigpond mail. They mangled the date and time information. It was fine going into their SPAM filter and Rubbish when it came out. They blamed my copy of Outlook which was not installed.