Hyatt owners have exclusive right to their unit from 1 year to six months out from their week. Although they can trade in their unit for points at any time, most don't. Their unit is converted to points at the six month mark, whether they like it or not. That's typically when Hyatt inventory becomes available. People have their week converted and kick them into Interval so they have more time to procrastinate.
Hyatt Maui (HKB) is special in that they have float weeks (and I don't know how their float reservations work -- Kal does). And they're special in that they're still a new resort and everyone wants to go there because it's a new Hyatt.
I think the chances of trading into HKB through Interval are somewhere between "slim" and "none." And even when I was trading into Hawaii constantly (to scout out possible locations for retirement), there is no way I'd bother with HKB. It would cost me a slew of Hyatt points for a week -- if I could even get a full week, which is unlikely. I can grab
five studio weeks in Interval for the same points as one week at HKB.
In the hopes of helping
@CalGalTraveler, I can say with confidence that "the resort basically doesn't matter." (I also haven't stayed in Kauai Beach Villas, which is in apparently really bad shape). I've stayed at a dozen timeshares on every island except Oahu (because I know that Oahu isn't for me). All of them have been fine. Some nicer than others. But not once have I said, "this is unacceptable, I'd rather stay in a hotel."
The very worst of the bunch had dated appliances. That's it. Dated appliances. No big deal. Grab a week in Hawaii. (I recommend Kona Coast Resort on the Big Island -- then you can visit my farm. I'm just up the road.) Any island is going to be fun. And except for a handful of exceptions, all the resorts are (at the very least) "good enough."