I just got Mrs DavidYYC an upgrade (as my nominee with no status) at exactly the 96 hour mark on AC 850 YYC-LHR.
I think (could be wrong though) that if there is no-one on the wait list, it is first come first served for E and their nominees to fight it out at the 96 hour mark.

The R number on this flight changed from R3 to R0 after the 7 day mark the back up to R1 then R2, before I upgraded.

If it was R1 when I did the request and there was another E who wished to upgrade themselves at the 96 hour mark, they would have lost out as my non status nominee got the last R seat at exactly the 96 hour point, he/she would lose out if their request came after mine.
There is no way that the system would know who wants an upgrade along with my nominee, until it is requested.