Intervals limits the viewing, editing, and approving of other people’s timesheets to only administrator level users. This is by design. A person’s timesheet captures time across multiple projects. A manager level user may or may not have access to those same projects. An administrator level user, however, is able to view all people and projects, and therefore, all timesheets.
While they can’t view other people’s timesheets, manager level users can see other people’s time by running a report. Time-based reports will display time entries for people who have access to the same projects as the manager running the report. In particular, the Summary report is quite similar to a weekly timesheet and has proven to be sufficient for most of our customers who ask us how they can see other people’s timesheets.
If the Summary report does not work for your use case, consider promoting the manager to an administrator level user with limited admin rights.