The project managers reviewing time cards for their team are able to see the billable hours submitted by them. However, they aren't able to review and approve any general overhead time. Why is this so?
When submitting time and expenses, Core provides four options: Specific, Client Manager, Project Manager and My Manager. When you select the Project Manager option, your time and expenses are submitted to the respective project managers assigned to the projects. So the overhead time in this case is submitted to the Project Manager of the 'Overhead' contract type project that your company must have set up. To change this, you need to set this project manager for the relevant overhead project in the Projects screen.