Multiple Timesheet Approvals - Multi-Layers for reviewers and approvers

Hi - it would be great if Timesheets could follow an approval process, so there could be reviewers and approvers.

In most places, the project managers would want to review all hours, and then managers would approve.

I cannot find a way to currently do this, and you already have an approval process function - can we add timesheets to be able to do this as well?