Just wondering again...
When a user logs in a sessions is created and a record in the sessions table.
The session is cleared when user logs out properly or by the cleaning job.
You could create a custom object to store the data from sessions and populate that with a process just before the job runs.with just one record for each user for a day. If that misses too many of the properly closed sessions the process could be run more frequently say hourly during peak hours.
Then you could have another process to check if there were any new records to the custom object during the past day and if there were you could xog in the date to a custom field of the resource object.in
Eventually you could display that in the standard resources list view..supported to me.
Far fetched, but appears supported to me