Y'know what? I think I know the reason for the discrepancy. I was looking through the event calendar and noticed a difference between event postings. When I post a podcast event, I include the date and time in the title (for previously-mentioned reasons), but for awhile one of the site volunteers was posting them shortly after I had my second kid and was busy with school projects/midterms/etc. His method didn't include the time information in the title and if I'm not mistaken, the email invites sent out are essentially copies of the event posting. Anyway, thanks for the information and I'll pass it on to the podcast volunteer group.
3 people RSVP'd, 30 showed up. That's pretty typical, actually.
Anyway, on the title of the event it says, specifically, "10pm EST." Eastern Standard Time. The event location is listed as "worldwide" because it's on the internet. I'd modify the time information on the event calendar to specify the Eastern time zone, but unfortunately the controls don't allow me to do so. The reason Eastern time is used as the time on the title has more to do with the site hosting the podcasts than personal preference.