AirNZ's position was that they knew about the change in coordinates straight away, because they did it deliberately, thinking that they were correcting a small error. The penny didn't drop until they discovered that a flightplan of the previous route had been floating around at the briefing. I'm reasonably sure that it took several days for that to be discovered.
On the day after the accident, all AirNZ had was an unmitigated disaster. They did not immediately hone in on navigation. Maintenence records were checked. And fuel. And crew medicals - and everything else, including navigation.