Blackouts is the possible elimination of car rental availability, special reduced rates, waivers and coupon usage from discounting web sites such as this one as well as the major brand car rental company retail websites. Sometimes these are called blocked time periods.
If your vacation in Hawaii begins within a blocked periods, when you attempt to reserve a rental car, the company reservations page may state a particular vehicle is unavailable altogether or only available at a higher rate.
When a car rental company retail website has a blackout, it usually means they won't accept coupons or have specials that fall within those dates. Some companies are lifting or eliminating some blackout dates as far as coupon usage is concerned because customers complained that the balckout time period is exactly when they needed or wanted to use the coupons the most.
Some national brand rental companies like Avis and Budget have set blackout periods during heavily traveled holiday dates. Also, Avis and Budget may have a shortage of vehicles to rent at various times during the ear. There are times where large groups or conventions come to certain Hawaiian Islands or large rental markets on the mainland. During those times Avis and/or Budget will close out some, most, or all vehicles available on their website to accommodate these commitments at that particular location. Other companies, like Dollar and Thrifty not only have blocked periods during heavily traveled holiday dates, in certain large markets like Hawaii, they also have floating blackout periods if they are heavily booked and there is a shortage of rentals availability.
If you are trying to rent from a company that has a date blacked out during the time you want to travel, simply check a different company or change your travel dates.
I used to find that if you alter your drop off time instead of having it be the exact same time that you pick up your vehicle, sometimes there was a huge difference in the cost of the rental. I haven't seen that a lot lately. I think the auto rental companies fixed that glitch.