Given HA's attitude of late, I think they'd ding you for the change fee, which would be at least $25. Since you're on a separate ticket, and since your connection is below the MCT, I just don't think they're likely to grant you "mercy" here. Right now flights are pretty full inter-island, and you would hate to end up spending time at the airport waiting for a spot to open up (once this year when a 6 hour meeting turned into a two hour one, I sat through three outbound departures that were totally full and ended up on my original, even though I was on the standby list -- which HA does only for those with HA status).

The likelihood is that you'll pay at least a $25 change fee if you miss your booked 25 minute-connection flight, and it could be much worse if there are few/no seats in a reasonable time.

Pay the $25/ticket up front and you'll have peace of mind.

If you have UA miles, you can also use them for 10K for a round-trip, or 5K for a one-way.