Potential ideas:

Hard statistics:

• using timestamps to compute ratio of messages in certain time interval
• using join time/leave time to compute user´s time online over certain period of time
• limit channel history checking to certain time interval
• limit channel history to certain scope of users (people from same team, admins...)
• finding the moment where conversation had most messages for certain time interval

Soft statistics:

• identify dialogs
• statistics for dialogs (length, participants..)
• analysis of dialogue - keywords, named entities, topics