Historically, Standby priority has been determined by three things according to the gate monitors: 1) Status, 2) Check-in time, 3) Travel disruptions, although exactly how being a distressed pax factors in is not entirely clear. However, with the change earlier this year to Upgrade priority, which no longer factors in Check-in time but only Purchase date, some have hypothesized that Check-in time also no longer matters for Standby priority, since they are both managed on the same PALL list behind the scenes.
However, there is no evidence as to whether or not such a change has been made to Standby priority. Barring that, I continue to operate under the assumption that Check-in time DOES matter for Standby priority and continue to do OLCI at T-24 (or thereabouts now that Upgrades are no longer impacted).
The 'real list' that the GA may have been talking about is the PALL list, which includes Upgrades, Standbys, Nonrevs, etc. Search for threads and posts by jrhone and you'll find more info, although some of it is apparently now dated.