An amendment to DIRA was passed into law earlier this year to clear the way for the earlier review and to ensure the market muscle of Fonterra would continue to be managed.
Before the amendment, the efficiency and contestability provisions of DIRA were due to expire in the South Island later this month, because its milk market there was now deemed competitive.
But the Commerce Commission in 2016 concluded competition was not sufficient to remove the DIRA provisions.
O'Connor also advised that the review, which was to take 12 months, was not a rehearsal for the scheduled 2020/21 review, as many in the industry thought.
"By rolling over the Act and committing ourselves to a wide-ranging review we are taking a considered and strategic approach to the changing needs of the dairy industry," he said at the time.