So the very responsive NEA site has chosen to emphasise the 24-hour PSI values in the respective zones. You have to scroll all the way to the bottom to see the trends for 3-hour PSI.
Is it really less relevant as they claim? I do not think so. An average over the last three hours, although already lagging, provide a better picture of what the air has been like. Of course, it does not include PM2.5, which is the more important value to look out for.
Then the question would be, why not use the AQI instead?