Delta changed the upgrade system back in May 2017 to open the windows at the precisely designated time for each flight segment. They no longer do the batch processing of upgrades at 5PM the day before your window opens and the flight segments are treated independently.
Yeah, this is kind of what I thought (and turned out to be correct - I was upgraded to C+ at +72 from the departure time for the second leg).
I was more interested in the fact that Delta thought my trip had already started, when it clearly hadn't.