The Unsubmit button will not appear on the timesheet which is in Open (not yet submitted for approval) and Approved status, even though it is enabled in the users Permissions. It will appear only when the timesheet is in Waiting for Approval status.

Note:
The purpose of the Unsubmit button is to retrieve a submitted timesheet before it has been approved, make corrections on the timesheet and resubmit it for the approval.