how can you tell how much time someone has been on the database?

If you have the appropriate plan and if you are a realm admin, you could see this information from audit logs. Once in a while, you could have that dumped into an Excel, absorbed into a table and then generate reports or see whatever it is you want from that data.

For more information about audit logs, visit https://help.quickbase.com/user-assistance/audit_logs.html

Hmm...good to know.  Thanks.  Not sure how to go about that, but I'll see what I can find out.  

Very helpful.  Thanks!