Note that the NSW Environment agency only reports the PM2.5 level as a 24 hour average, which can make it really difficult to find out what the actual air quality is in real time. However, since visibility is also reported as a 1 hour average, and it is a much better metric for determining the real time quality of the air, the AQI calculation has been updated to take into account the visibility.
For instance, the PM2.5 24 hour average can be Good in Sydney, but the Visibility could be well past Hazardous. In this case, it would take several hours for the PM2.5 24 hour average to report as hazardous because there could have been a fairly good air quality over the last 24 hours and only just recently has the wind started to blow the smoke towards Sydney.
So basicly look at the visibility NEPH readings (not the PM2.5 reading) for an up to date measurement of current air quality including estimate of current PM2.5 levels. Or just look out your window