This will get you pretty close. Go:
Organisation/Summary Report
Make sure you are using the "new" version. There is usually an option to switch in the top right hand corner.
You can now generate a summary part for the "Entire Organisation" for a specific SSID for a summary time frame.
![Screenshot from 2018-01-17 18-02-40.png Screenshot from 2018-01-17 18-02-40.png](https://community.meraki.com/t5/image/serverpage/image-id/1430i11354DF85A80EAF9/image-size/large?v=v2&px=999)