Crowds would be heaviest when traffic is lightest (weekdays for less crowds, but more traffic...weekends/holidays for more crowds less traffic.) You could always get lucky on a weekend and the crowds might not be too bad, or on a weekday you can dodge traffic by avoiding rush hour. Thats for diamond head and pearl harbor. For these, its kinda a pick your poison (traffic or crowds) or be willing to wake up very early (before 5:30 am on a weekday at the latest) and plan something near by till parking opens. You’ll probably not see the worst of the traffic in the mornings as some schools will be out for summer vacation at that point...but highschool graduations are a big thing so friday through sunday could see some very heavy traffic in the afternoons. It will also quite likely be very hot...so diamond head after 10 am could be...more difficult of a hike than it otherwise would be.
Kualoa ranch wouldn’t have as much issues with traffic, and its more or less the same thing as polynesian cultural center as far as crowds (i.e. almost all tourists so day of week doesn’t matter quite as much). On weekdays you still have to fight quite a bit of traffic in the morning, but you won’t have to fight it the whole way there.
