My topic was moved from Technical Support to General Discussion, even though this isn't a Discussion Topic. I hope that explains why this had the appearance of being posted after the event had ended.

The only thing I can think is that the event logged your initial log-in based on PST (which was not mentioned in the Event Page) rather than Local Time.
Which is patently absurd, to make an event's start and end times based on split time qualifiers. But that's a topic for the game team to address, not the community.
But if that is, in fact, what happened, then my December 19th log-in was not at a time when it was also December 19th in California (PST). In which case, if I had waited three measly hours, I would have actually had the full intended log-in time. But because I failed to scry the time zone truth from my crystal ball... I was too excited and cost myself an entire day of play. Happy Holidays to me.

I assumed that, given the log-in period ended at "11:59 p.m. (local time)", the start time would also be logged in local time. That made sense to me, but was clearly incorrect.

But it's all moot now, since the event is absolutely over, and it took until my issue quite literally timed out of relevance to get a (non)response.

I appreciate you trying to help Iscah. "Something strange with time zones" is what I'm banking on.
Hopefully future events will have more clarity to their terms to eliminate this sort of confusion, error, and disappointment.