KORH is operational 24hrs, however the tower has limited operational times. The only FBO on the field has a callout charge of about $250 if you need their assistance outside of their operating hours. That said, I did arrive close to 11PM and the person at the FBO was accomodating as she could be and managed to avoid that fee.
not sure what you mean by "open" I think that they're open when there are flights going in and out but if you randomly show up at 3am the doors may be locked
No, check the airport website for terminal hours
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