>>>>>>One thing to keep in mind is that there is clearly an EUA that is run in the early morning day of depature.
>>Just curious - is this an established fact or speculation?

I've been upgraded in the early AM prior to flying numerous times in the past year--it is very predictable--like clockwork for those flights that are actually half empty in F where they will be upgrading a handful of elites in any case.

It generally happens 6am or 7am. Oddly, as opposed to normal days-out EUA's that pop me into a seat, these early morning day-of-travel EUA's always wind up saying "seat unassigned", and I have to select a seat. This suggests that this is a 'different' kind of upgrade--it may in fact be a processing of the waitlist--it's hard to know (I always abort check-in at 23:59 after being told that I have been put on the waitlist). It is also completely possible, maybe even likely, that people who DID check in already, and who are also in good shape on the waitlist, are ALSO being upgraded within the system, but will receive their F boarding passes at the gate--nobody knows. Even if this turns out to be the case though, I still prefer getting the upgrade in the morning so that I can select my own seat.