A Gurteen Knowledge Café usually runs for 1 1/2 - 2 hours in total depending on how much time available. It is impossible to run one in less than 1 hour. The ideal number of participnats is 16 - 24. Any more than 30 means it is impossible to hold the whole group conversation at the end without the need for microphones which somewhat curtails the dynamics of the conversation.
The only hard and fast rule is that the meeting is conducted in such a way that most of the time is spent in conversation - it is not about one person presenting to the group.
A simple session may go something like this.
Optionally, the facilitator gives a presentation on what knowledge cafes are all about and the role of conversation in business life. (anywhere between 5 mins and 1 hr with a few conversational exercises). I usually only do this at a conference where people are not already familiar with the concepts and this turn the whole event effectively into a half-day workshop.
The facilitator welcomes people to the Café - about 5 mins.
The facilitator spends 10 - 15 minutes outlining the subject or theme of the Café and poses a single open-ended question.
e.g. if the theme is knowledge-sharing then the question for the group might be 'what are the barriers to knowledge-sharing in an organization and how do you overcome them?'
The group breaks into small groups of 3-4 (no more than 5) and discusses the questions for about 45 mins and then we come back together as a whole group for the final 45 mins where the individual groups share their thoughts. Optionally in the small group sessions, people change tables every 15 mins to broaden the number of people they get to interact with and thus the differing perspectives of the group.
Usually no attempt is made to capture the conversation as doing so tends to destroy the conversation. The value of the Cafe is in the conversation itself and the learning that each individual takes away. In some circumstances though it makes sense to capture things from the Cafe depending on its purpose and there are ways of doing this that interfere minimally dynamics of the conversation.
You can learn more on my dedicated Knowledge Café website.