Have you experimented with doing this manually at all yet? Knowing now that works in practice would be helpful for designing built in features for this.
I could imagine doing something like with existing features:
- create a category for these kinds of channels that is associated with a group people can join freely to gain access
- create a topic in the category about the upcoming event
- at the desired time, create a channel I’m that category with auto-join enabled
- @group in the topic to let folks know the channel is open
- chat away in the channel
- Use the archive channel feature to capture the transcript in the topic.
If folks try that out or something like it I’d be interested to hear how it goes. What works well, what could be better, etc.