Please don't add new answers. I don't understand how overlapping answers are supposed to be handled.
If the hike does not take place or is postponed it will resolve to N/A.
Attendee is anyone who joins for at least 30 minutes with the express purpose of participating in this "Rationality Freiburg" event.
The intervals are closed (include the endpoints) e.g. 6-8 is correct if and only if 6 people, 7 people or 8 people attend.