To add to the comments (and
FlY2XS is more the expert in this particular region), calling directly is definitely advised for regional car rentals like this. The car I am currently driving was not officially available for pick up at the time my flight arrived in YXJ because websites all showed the agency as "closed" at that specific time. It most certainly was not. In general for these rural airports they will have staff to meet all incoming flights for rental pick ups, even if their own website indicates the station is "closed", but booking in advance is essential because there aren't always cars available and if no one is scheduled for a rental there might not be staff. Sometimes the staff members just come in for the 45-1 hour post arrival, then vacate the location again.
**Slightly off topic, but the shortage of car rentals is a much discussed issue in other forums - largely due to fleets being sold off to liquidate assets and there not being availability to replace fleets at the rate they were sold now that things are picking up, not limited to HI, but all over NA.