Naha airport when to leave?

I will stay along the monorail near central Naha having an evening domestic flight to Tokyo. Not sure when better be at the airport to have time for check in, security etc.

I have only travelled from Haneda once and I remember being at the airport about an hour before departure. But that was a morning flight and check in opened just a few minutes after I got there...

I think the monorail takes 10-15 mins to the airport.

Flight departs 18:00 if I remember correctly. Should I leave by train perhaps 16:45? Or too late?

16:45? ought to be fine. I personally would allow more time, as to avoid any unforeseen circumstances.

Oh, I thought Naha airport was quite small so not so much need for time as other airports but maybe I was wrong...

It is small, but I would allow more time for any flight. That is departure time, not the latest time you need to be there. Personal preference though.

Let us know what you decide and what you recommend to others.

I personally always find 1 h for domestic or EU national flights sufficient. Never missed any flight.

I was looking back through some photos and did a domestic flight from Fukuoka to Sapporo, leaving 14.25. I was actually on my way to Hakata subway station about 13.10, not exactly sure when checking in but I was boarding by 14.10. I suppose add 15-20 minutes from outside Hakata, about 55-60 mins before departure.