Ann: Suspension from Official Quotation, page-309

Stocks on ASX have staged starting times based on alphabetic order. + a 30 second buffer at random.

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Opening takes place at 10:00 am Sydney time and lasts for about 10 minutes. ASX Trade calculates opening prices during this phase. Securities open in five groups, according to the starting letter of their ASX code:

Group 1 10:00:00 am +/- 15 secs 0-9 and A-B, e.g. ANZ, BHP
Group 2 10:02:15 am +/- 15 secs C-F, e.g. CPU, FXJ
Group 3 10:04:30 am +/- 15 secs G-M, e.g. GPT
Group 4 10:06:45 am +/- 15 secs N-R, e.g. QAN
Group 5 10:09:00 am +/- 15 secs S-Z, e.g. TLS

The time is randomly generated by ASX Trade and occurs up to 15 seconds on either side of the times given above, e.g. group 1 may open at any time between 9:59:45 am and 10:00:15 am.
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https://www.asx.com.au/about/trading-hours.htm