It is possible that your first flight will be on time, and that you will be able to walk to your connecting gate in time to catch the interisland flight, although it would be pretty tight. Note that if the doors open at 5:50, it may well be 6:00 before you get out of the jetway, depending on where you are seated. If your NW flight is late, this gets worse.

What seems pretty unlikely, however, is for your baggage to make it onto a 6:35 HA flight. If you make it and your bags don't, you can wait in KOA for the bags to come in on a later flight or hope that they are delivered to you, probably the next day.

It seems like it would be less stressful to book the later flight.