There are several approval options and the exact behavior of the timesheet system depends on which option your organization uses. There are the following players in the approval process:
PM Approver (Project Owner) - If your organization has configured PPM Pro to include project managers in the timesheet approval process (2-step approval), then the project owner approves project time entries for project team members.
Final Timesheet Approver (specified in the Timesheet Approver field on each resource's Info page) - Approves timesheets that have already received PM approval of project time entries (if using 2-step approval process). If using 1-step approval, Final Timesheet Approver approves all timesheets directly.
(optional) Alternate Final Timesheet Approver - Can approve timesheets if the regular approver is unavailable (specified in the Final Timesheet Approver's Info page - Alternate Timesheet Approver).
(optional) Time Admin (member of Admin Timesheets team) - Can step in at any point and edit/submit/reject/approve a user's timesheet.
Every resource record has a Timesheet Approver field, which is where you specify the final approver for the resource.
To configure the Alternate Timesheet Approver, go to the resource record of the Final Timesheet Approver and enter a user in the Alternate Timesheet Approver field.
For example, if "Jane Doe" is a Timesheet Approver for a set of resources (her name is in the Timesheet Approver field for each resource) and you want to specify Jackie O as her alternate, you would navigate to Jane Doe's resource Info page and enter "Jackie O" in the Alternate Timesheet Approver field. Jackie O can now approve timesheets for Jane Doe's people.
The project owner is the PM Timesheet Approver. To specify an Alternate PM Approver, go to the Settings page of the project and enter a value in the Alternate PM Timesheet Approver field.