With the community manager reports, you can look at the last 7 days or create a custom date range:
However the Community Manager Reports are not recorded in real-time. Each morning, generally around 1am, the ETL's run and the actions from the previous day are recorded. Therefore a one-day delay will always be present.
With that said, if you are Cloud Customer or have Cloud Analytics enabled, the DES is much closer to real-time, and might be an alternative you might consider. These documents provide more on the DES https://community.jivesoftware.com/docs/DOC-99916#jive_content_id_How_many_users_logged_in_during_the_last_hour and How To: Use the Data Export Service API Explorer
More specially, it provides an example for pulling the number of logged in users for a specific timeframe:
- period: lasthour, lastday, lastweek
Hope this helps.