BHP and RIO better for dividends now over FMG, page-12

If you receive a dividend you just need to hold the share for at least 45 days. For example that means you could be holding it 20 days before ex-div and then 26 post receiving payment. On the 46 day of holding that share if you sold than you would receive the franking credit tax offset. Note if you sold on day 45 or less you would not be entitled to receive a franking credit tax offset in your assessment (unless you qualify for the Small Shareholder Exemption - which allows shareholders who received total franking credits that is less than $5,000 for the financial year to claim their franking credits in their tax returns, even when they may not have held the shares at risk for 45 days.

https://www.ato.gov.au/Forms/You-and-your-shares-2021/?page=10
"Holding period rule
The holding period rule requires you to continuously hold shares ‘at risk’ for at least 45 days (90 days for certain preference shares) to be eligible for the franking tax offset."

This is not tax advice, DYOR.