I have stayed for a month or so in Waikiki for the last four years. Every morning I check for availability through RCI weeks and see plenty of availability with less than two weeks out at about half the TPU’s. Usually around 20 to 24 for a studio or one bedroom. Sometimes as low as 12! This has worked out well for us and I brave the uncertainty in order to stretch out my TPU’s.
Available units are at a premium in February/March/April, but I have been able to book last minute with no huge glitches so far. I have done this in November, December and March April. Generally I might have to book a few nights at a hotel to fill the gaps in and moving around can be a pain. I like Lifetime in Hawaii for its free parking, Imperial Hawaii for its location and super friendly staff, Royal Aloha Lewers Street for the in unit washer and dryers and warm pool.
I do have an advantage in car usage as I borrow my daughters car for the period that we are there. I can also stay at her apartment if need be, although I really like having my own place to stay. I’ve done some serous studying on availability and belong to RCI, DAE, II and frequent Hawaii Timeshare exchange as well. I must have a unit that sleeps four so a few of the timeshares that are available do not fit my needs such as Royal Garden. I also have found that some timeshares within the same building (Royal Kuhio) can have widely varying extra fees...so be careful. Happy Hunting!