Metered parking is free from 6PM on. So as long as it's after 4, you can feed the meter until 6 and are set all night. The meters take credit cards now. I think the closest, most likely to be available metered parking would be right in front of City Hall or on Jackson just east of the back of the Grand Bohemian Hotel.
If anyone is coming from Winter Park or Seminole County and was curious about trying SunRail, the schedule might work out well for this event and you can't beat the train station location right next to Church Street. Southbound train arrives at Church Street at 5:51PM and there is one leaving back north at 7:40PM. I say might because I'm not sure if this is a 2 hour program or more of an open house where it would be okay to leave around 7:40. (Next train north isn't until 9:25)