salesforce wont log Logout times , we can really see the Login Date and Time. Without a logout time it's not possible to determine how long they have been in the system.
But there is a solution on the AppExchage that tracks the actual time your team spends on their sessions within salesfoce. here is the link which may help you app called ::Time Tracking
But there is a solution on the AppExchage that tracks the actual time your team spends on their sessions within salesfoce. here is the link which may help you app called ::Time Tracking
https://appexchange.salesforce.com/listingDetail?listingId=a0N300000016bTgEAI