For many - though not all - companies, to find such dates, go (typically) to 'investors' on the website, and look up 'calendar'.
TGR's indicates that final results will be reported on either 18 or 19 August 2021. I'm unsure why it is hedging its bets between two dates.
Quite often, companies will issue an announcement at some time between 0800 and 0930, prior to the market's official opening at 1000 AEST.
Keep an eye on both dates. With 'HC', the announcements are delayed by 15 minutes but on what I find to be the excellent nabtrade, one has a red button pop up against the stock name if one holds that stock and voila - one click and the announcement appears prior to it becoming viewable on 'HC'.
TGR Price at posting:
$3.36 Sentiment: Hold Disclosure: Held