The preview of results is gradually rolled out over 24 hours.

[yi-ing]

The preview of IELTS test results will start at 5pm Australian Eastern Daylight Saving Time (AEDT) on the 13th day after the test unless otherwise specified in the information provided by your test centre. The preview of results is gradually rolled out over 24 hours.

Does the bold part mean "it takes 24 hours from Australian Eastern Daylight Saving Time (AEDT) to get the IELTS result"?

 

[teechar]

Does the bold part mean "it could take up to 24 hours from 5 pm Australian Eastern Daylight Saving Time (AEDT) on that day to get the IELTS result"?

That's what I take it to mean.