The announced record date is 7:00pm 8 March 2019.On my reading...

The announced record date is 7:00pm 8 March 2019.
On my reading of the link provided by Swage, to be eligible, you needed to be a registered holder at that time,
In normal circumstances with a two day settlement of market transactions, that would mean that you would have to have acquired APX at least two days before that date, that is on or before 6 March.
In other words, as with dividends, the "ex" date is normally one trading day before the record date, which means to be eligible you needed to have bought an APX share on the day before the "ex" date, ie 6 March.
Simples!

Please correct me if I am wrong.

As swage said, given the enthusiasm for the stock and the paltry amount allocated to the SPP, the $15m to be raised in the SPP could well be overwhelmed with subscriptions and scaled back to homeopathic quantities.

Cheers