Yes, you can make an employee an approver.
- Click on Setup under Preferences
- Click on Approval Workflow
- If you want Employee's Manager to approve time, select Employee's Manager under Employee's time must first be approved by and then click on Assign Employee Approver, in the pop up select Approver for each employee. The approvers here are employees of the company.
- You can follow the same steps for Project Manager, Time Off, and Expense.