Typically, the meetings lasted 1/2 day to 2 days for the entire membership, and some meetings included separate sessions for smaller groups to discuss specific technical or member issues.
The meetings lasted up to 12 days for everyone. 
mnli hypothesis: The meetings lasted up to 12 days for everyone.  premise: Typically, the meetings lasted 1/2 day to 2 days for the entire membership, and some meetings included separate sessions for smaller groups to discuss specific technical or member issues.