I'm going to the Big Island (KOA) for 6 nights and am debating whether to stay in Honolulu for one night since my flight back to mainland is in HNL.

Is there enough time to "explore" the city?
Option 1:
I was thinking of flying from KOA to HNL at noon the day before and rent a car to explore the HNL. However, I would have to return the car at the latest at 3PM (with grace period), but my flight back to mainland is on CO at 7:50PM (too much time at the airport).

Option 2:
If I take a later flight back to HNL (at 3PM), I can return the car at a later time which is closer to my CO departure time, but I'll end up with less time in HNL compared with option 1.

Option 3:
Or should I just skip HNL altoghter and spend all my time in KOA?