If I recall my scrip days in banking the payment date is the company elected date, and what you will find is that a tape (or similar medium) would be passed to the banks ahead of the payment date as beneficiaries have already been identified as the last day to register has already passed. The banks then credit their clients, in my case my shares are in nominees so the company does not know that I am a shareholder. My dividends are always paid on the payment date or 1 day prior to payment date, but, never late. Also it depends how you elect to receive your dividends - if you elect to receive into a current account (as an example) then that has to be processed through the data processing systems of the banks. If you elect to have the dividends paid into your trading account then there is no delay in terms inter bank exchanges.
So I suspect that maybe those persons who elect to receive dividend to an account other than their trading account with their broker that they could end up with a delay due to the interbank exchange system which would delay dividend receipts by 24 or 48 hours
