Hey @bekka - I quickly had a look at the event and saw it was created under your profile:
That normally means that only you can start the hangout - it doesn't automatically start when you schedule it unfortunately.
I created another event using the P2PU Google+ page profile. It is what you get when you switch to the "P2PU Google+ page" profile in the dropdown. I need to first switch into my @p2pu.org account before I can switch into the page profile.
I updated the link above to point to this event
Please try switching into the page profile and let me know if you can edit the event.