I was just able to score reservations at 'Ohana and checked about 15 minutes ago. There was always a "9:45" time but that was too late for my party.
I've been checking reservations at least 4 times a day (when I wake up around 8, around lunch, dinner and then before going to bed around 11) Also checked on the weekends at various times and if I got bored at work.

I've been trying for about 4 weeks.
Reservations seemed to "change" the most (9:45 became 9:30 or one time 8:45) around the weekend (Saturday night/Sunday morning, Sunday night/Monday morning and sometimes early evening during the week (around 6pm).
That makes sense to me because the "organized" people would probably be doing it after work or on the weekend.