Users and their browsing time can be found in the Productivity Section of our 'Overview Reports'. However if you want to see the username, website and browsing time, then this is best viewed in an Activity Report (Go to Reports | Activity Report)
Activity Reports force you to enter at least one filter, as they do return quite a lot of information. But to run an Activity Report on _all_ users, try the filter: Action 'Equal to' Allowed
This will return a list of all users, the websites they visited and the browsing time of each, throughout the day.