Re: Can SD add the usage time of sessions of a user?
I do not think the application itself can do it.
You could take advantage of Enhanced Auditing, which can keep track of session login/logout. Then use the Generated Views for Reporting, query the auditlog view for a particular user or set of users during a certain period of time or specific day.
Ater that, export to Excel to calculate duration times between the Login and Logout entries and finally sum all the duration times.