Others on this and related threads have noted that their experience has been that, at least domestically, flights with R=0, F>0 seem to go to R=F slightly earlier than T-24 hr with some consistency. I booked a flight with F=5, R=0 2 months out and waitlisted a RPU. Watched closely every day as flight dropped to F=2 a few days out; not surprising IM leaves R=0. Emboldened by FT, at T-25 hrs I started to watch R every minute or so (ok, it was a boring meeting, and with KVS Tool it's just one click to refresh and look). At precisely T-24:30, flight went to R=2, F=2. I stepped out of the meeting and called UA. Competent lady cleared R for me within seconds, no arguing about needing to wait to have WL clear, etc. Stepped back into meeting. Saw F=R=1 (my own seat clearing, presumably). One minute later, F=R=0 (another FT reader?). I don't believe for a moment this was auto clearing of the WL. If I had waited until T-24:25 rather than 24:30 to check, I'd be sitting in the back. (Lucky I didn't have to HUCA!). And on flight day there are >50 pax waiting for CPUs with F=0, some of them no doubt outranking me and willing to have used instruments rather than CPU.

I've become a believer -- from now on, I'm there at T-24:35 or so, unless I'm airborne. Stupid system? Unfair system? Absolutely. But to paraphrase an infamous VEEP, we don't fly the United we want, we fly the United we have.